Oracle Programming/SQL Cheatsheet
This "cheat sheet" covers most of the basic functionality that an Oracle DBA needs to run basic queries and perform basic tasks. It also contains information that a PL/SQL programmer will frequently use to write stored procedures. The resource is useful as a primer for individuals who are new to Oracle, or as a reference for those who are experienced at using Oracle.
A great deal of information about Oracle exists, scattered throughout the net. This resource was developed in order to make it easier for programmers and DBAs to find most of the basics in one place. When a topic is beyond the scope of a "cheatsheet" a link is generally provided for further research.
Other Oracle References
- Oracle XML Reference - the XML reference is still in its infancy, but it will be coming along nicely before long.
SELECT FROM Namibia WHERE col1 = 'value1' AND col2 = 'value2'
Select into takes the values name, address and phone number out of the table employee and places them into the variables v_employee_name, v_employee_address and v_employee_phone_number.
This only works if the query matches a single item. If the query returns no rows it will raise the NO_DATA_FOUND built-in exception. If your query returns more than one row, Oracle will raise the exception TOO_MANY_ROWS.
SELECT name,address,phone_number INTO v_employee_name,v_employee_address,v_employee_phone_number FROM employee WHERE employee_id = 6;
insert using the VALUES keyword
INSERT INTO table_name VALUES (' Value1', 'Value2', ... ); INSERT INTO table_name( Column1, Column2, ... ) VALUES ( 'Value1', 'Value2', ... );
insert using a SELECT statement
INSERT INTO table_name( SELECT Value1, Value2, ... from table_name ); INSERT INTO table_name( Column1, Column2, ... ) ( SELECT Value1, Value2, ... from table_name );
The DELETE statement is used to delete rows in a table. deletes the rows which match the criteria
DELETE FROM table_name WHERE some_column=some_value DELETE FROM customer WHERE sold = 0;
updates the entire column of that table
UPDATE customer SET state='CA';
updates the specific record of the table eg:
UPDATE customer SET name='Joe' WHERE customer_id=10;
updates the column invoice as paid when paid column has more than zero.
UPDATE movies SET invoice='paid' WHERE paid > 0;
Setting Constraints on a Table
The syntax for creating a check constraint using a CREATE TABLE statement is:
CREATE TABLE table_name ( column1 datatype null/not null, column2 datatype null/not null, ... CONSTRAINT constraint_name CHECK (column_name condition) [DISABLE] );
CREATE TABLE suppliers ( supplier_id numeric(4), supplier_name varchar2(50), CONSTRAINT check_supplier_id CHECK (supplier_id BETWEEN 100 and 9999) );
Unique Index on a Table
The syntax for creating a unique constraint using a CREATE TABLE statement is:
CREATE TABLE table_name ( column1 datatype null/not null, column2 datatype null/not null, ... CONSTRAINT constraint_name UNIQUE (column1, column2, column_n) );
CREATE TABLE customer ( id integer not null, name varchar2(20), CONSTRAINT customer_id_constraint UNIQUE (id) );
Example CREATE TABLE OOP (ID NUMBER(20), NAME VARCHAR2(20));
SQL> ALTER TABLE OPP ADD COBSTRAINT OPP_ID_UK UNIQUE(ID);
The syntax for a sequence is:
CREATE SEQUENCE sequence_name MINVALUE value MAXVALUE value START WITH value INCREMENT BY value CACHE value;
CREATE SEQUENCE supplier_seq MINVALUE 1 MAXVALUE 999999999999999999999999999 START WITH 1 INCREMENT BY 1 CACHE 20;
Increment a sequence by a certain amount:
ALTER SEQUENCE <sequence_name> INCREMENT BY <integer>; ALTER SEQUENCE seq_inc_by_ten INCREMENT BY 10;
Change the maximum value of a sequence:
ALTER SEQUENCE <sequence_name> MAXVALUE <integer>; ALTER SEQUENCE seq_maxval MAXVALUE 10;
Set the sequence to cycle or not cycle:
ALTER SEQUENCE <sequence_name> <CYCLE | NOCYCLE>; ALTER SEQUENCE seq_cycle NOCYCLE;
Configure the sequence to cache a value:
ALTER SEQUENCE <sequence_name> CACHE <integer> | NOCACHE; ALTER SEQUENCE seq_cache NOCACHE;
Set whether or not the values are to be returned in order
ALTER SEQUENCE <sequence_name> <ORDER | NOORDER>; ALTER SEQUENCE seq_order NOORDER;
Generate Query From A String
It is sometimes necessary to create a query from a string. That is, if the programmer wants to create a query at run time (generate an Oracle query on the fly), based on a particular set of circumstances, etc.
Care should be taken not to insert user-supplied data directly into a dynamic query string, without first vetting the data very strictly for SQL escape characters; otherwise you run a significant risk of enabling data-injection hacks on your code.
Here is a very simple example of how a dynamic query is done. There are, of course, many different ways to do this; this is just an example of the functionality.
PROCEDURE oracle_runtime_query_pcd IS TYPE ref_cursor IS REF CURSOR; l_cursor ref_cursor; v_query varchar2(5000); v_name varchar2(64); BEGIN v_query := 'SELECT name FROM employee WHERE employee_id=5'; OPEN l_cursor FOR v_query; LOOP FETCH l_cursor INTO v_name; EXIT WHEN l_cursor%NOTFOUND; END LOOP; CLOSE l_cursor; END;
Instr returns an integer which specifies the location of a sub-string within a string. The programmer can specify which appearance of the string they want to detect as well as a starting position. If the search is unsuccessful then the return value is 0.
instr( string1, string2, [ start_position ], [ nth_appearance ] ) instr( 'oracle pl/sql cheatsheet', '/'); this returns 10, since the first occurrence of "/" is the tenth character instr( 'oracle pl/sql cheatsheet', 'e', 1, 2); this returns 17, since the second occurrence of "e" is the seventeenth character instr( 'oracle pl/sql cheatsheet', '/', 12, 1); this returns 0, since the first occurrence of "/" is before the starting point, which is the 12th character
Replace looks through a string, replacing one string with another. If no other string is specified, it removes the string specified in the replacement string parameter.
replace( string1, string_to_replace, [ replacement_string ] ); replace('i am here','am','am not'); this returns "i am not here"
Substr returns a portion of the given string. The "start_position" is 1-based, not 0-based. If "start_position" is negative, substr counts from the end of the string. If "length" is not given, substr defaults to the remaining length of the string.
substr( string, start_position [, length])
SELECT substr( 'oracle pl/sql cheatsheet', 8, 6) FROM dual;
- returns "pl/sql" since the "p" in "pl/sql" is in the 8th position in the string (counting from 1 at the "o" in "oracle")
SELECT substr( 'oracle pl/sql cheatsheet', 15) FROM dual;
- returns "cheatsheet" since "c" is in the 15th position in the string and "t" is the last character in the string.
SELECT substr('oracle pl/sql cheatsheet', -10, 5) FROM dual;
- returns "cheat" since "c" is the 10th character in the string, counting from the end of the string with "t" as position 1.
These functions can be used to filter unwanted characters from strings. By default they remove spaces, but a character set can be specified for removal as well.
trim ( [ leading | trailing | both ] [ trim-char ] from string-to-be-trimmed ); trim (' removing spaces at both sides '); this returns "removing spaces at both sides" ltrim ( string-to-be-trimmed [, trimming-char-set ] ); ltrim (' removing spaces at the left side '); this returns "removing spaces at the left side " rtrim ( string-to-be-trimmed [, trimming-char-set ] ); rtrim (' removing spaces at the right side '); this returns " removing spaces at the right side"
The syntax to create a table is:
CREATE TABLE [table name] ( [column name] [datatype], ... );
CREATE TABLE employee (id int, name varchar(20));
The syntax to add a column is:
ALTER TABLE [table name] ADD ( [column name] [datatype], ... );
ALTER TABLE employee ADD (id int)
The syntax to modify a column is:
ALTER TABLE [table name] MODIFY ( [column name] [new datatype] );
ALTER Table Syntax and Examples:
ALTER TABLE employee MODIFY( sickHours s float );
The syntax to drop a column is:
ALTER TABLE [table name] DROP COLUMN [column name];
ALTER TABLE employee DROP COLUMN vacationPay;
Constraint Types and Codes
|Type Code||Type Description||Acts On Level|
|C||Check on a table||Column|
|O||Read Only on a view||Object|
|R||Referential AKA Foreign Key||Column|
|V||Check Option on a view||Object|
The following statement will show all of the constraints in the system:
SELECT table_name, constraint_name, constraint_type FROM user_constraints;
select * table_name;
Selecting Referential Constraints
The following statement will show all referential constraints (foreign keys) with both source and destination table/column couples:
SELECT c_list.CONSTRAINT_NAME as NAME, c_src.TABLE_NAME as SRC_TABLE, c_src.COLUMN_NAME as SRC_COLUMN, c_dest.TABLE_NAME as DEST_TABLE, c_dest.COLUMN_NAME as DEST_COLUMN FROM ALL_CONSTRAINTS c_list, ALL_CONS_COLUMNS c_src, ALL_CONS_COLUMNS c_dest WHERE c_list.CONSTRAINT_NAME = c_src.CONSTRAINT_NAME AND c_list.R_CONSTRAINT_NAME = c_dest.CONSTRAINT_NAME AND c_list.CONSTRAINT_TYPE = 'R' GROUP BY c_list.CONSTRAINT_NAME, c_src.TABLE_NAME, c_src.COLUMN_NAME, c_dest.TABLE_NAME, c_dest.COLUMN_NAME;
Creating Unique Constraints
The syntax for a unique constraint is:
ALTER TABLE [table name] ADD CONSTRAINT [constraint name] UNIQUE( [column name] ) USING INDEX [index name];
ALTER TABLE employee ADD CONSTRAINT uniqueEmployeeId UNIQUE(employeeId) USING INDEX ourcompanyIndx_tbs;
The syntax for dropping (removing) a constraint is:
ALTER TABLE [table name] DROP CONSTRAINT [constraint name];
ALTER TABLE employee DROP CONSTRAINT uniqueEmployeeId;
See also: Oracle Constraints
An index is a method by which records are retreived with greater efficiency. An index creates an entry for each value that appears in the indexed columns. Oracle will, by default, create B-tree indexes.
Create an Index
The syntax for creating an index is:
CREATE [UNIQUE] INDEX index_name ON table_name (column1, column2, . column_n) [ COMPUTE STATISTICS ];
UNIQUE indicates that the combination of values in the indexed columns must be unique.
COMPUTE STATISTICS tells Oracle to collect statistics during the creation of the index. The statistics are then used by the optimizer to choose an optimal execution plan when the statements are executed.
CREATE INDEX customer_idx ON customer (customer_name);
In this example, an index has been created on the customer table called customer_idx. It consists of only of the customer_name field.
The following creates an index with more than one field:
CREATE INDEX customer_idx ON supplier (customer_name, country);
The following collects statistics upon creation of the index:
CREATE INDEX customer_idx ON supplier (customer_name, country) COMPUTE STATISTICS;
Create a Function-Based Index
In Oracle, you are not restricted to creating indexes on only columns. You can create function-based indexes.
The syntax for creating a function-based index is:
CREATE [UNIQUE] INDEX index_name ON table_name (function1, function2, . function_n) [ COMPUTE STATISTICS ];
CREATE INDEX customer_idx ON customer (UPPER(customer_name));
An index, based on the uppercase evaluation of the customer_name field, has been created.
To assure that the Oracle optimizer uses this index when executing your SQL statements, be sure that UPPER(customer_name) does not evaluate to a NULL value. To ensure this, add UPPER(customer_name) IS NOT NULL to your WHERE clause as follows:
SELECT customer_id, customer_name, UPPER(customer_name) FROM customer WHERE UPPER(customer_name) IS NOT NULL ORDER BY UPPER(customer_name);
Rename an Index
The syntax for renaming an index is:
ALTER INDEX index_name RENAME TO new_index_name;
ALTER INDEX customer_id RENAME TO new_customer_id;
In this example, customer_id is renamed to new_customer_id.
Collect Statistics on an Index
If you need to collect statistics on the index after it is first created or you want to update the statistics, you can always use the ALTER INDEX command to collect statistics. You collect statistics so that oracle can use the indexes in an effective manner. This recalcultes the table size, number of rows, blocks, segments and update the dictionary tables so that oracle can use the data effectively while choosing the execution plan.
The syntax for collecting statistics on an index is:
ALTER INDEX index_name REBUILD COMPUTE STATISTICS;
ALTER INDEX customer_idx REBUILD COMPUTE STATISTICS;
In this example, statistics are collected for the index called customer_idx.
Drop an Index
The syntax for dropping an index is:
DROP INDEX index_name;
DROP INDEX customer_idx;
In this example, the customer_idx is dropped.
Creating a User
The syntax for creating a user is:
CREATE USER username IDENTIFIED BY password;
CREATE USER brian IDENTIFIED BY brianpass;
The syntax for granting privileges is:
GRANT privilege TO user;
GRANT dba TO brian;
The syntax for changing user password is:
ALTER USER username IDENTIFIED BY password;
ALTER USER brian IDENTIFIED BY brianpassword;
Importing and Exporting
There are two methods of backing up and restoring database tables and data. The 'exp' and 'imp' tools are simpler tools geared towards smaller databases. If database structures become more complex or are very large ( > 50 GB for example) then using the RMAN tool is more appropriate.
Importing a Dump File using IMP
This command is used to import Oracle tables and table data from a *.dmp file created by the 'exp' tool. Remember that this a command that is executed from the command line through $ORACLE_HOME/bin and not within SQL*Plus.
The syntax for importing a dump file is:
There are number of parameters you can use for keywords.
To view all the keywords:
imp brian/brianpassword FILE=mydump.dmp FULL=yes
- Addition: +
- Subtraction: -
- Multiplication: *
- Division: /
- Power (PL/SQL only): **
gives all employees a 5% raise
UPDATE employee SET salary = salary * 1.05 WHERE customer_id = 5;
determines the after tax wage for all employee's
SELECT wage - tax FROM employee;
- Greater Than: >
- Greater Than or Equal To: >=
- Less Than: <
- Less Than or Equal to: <=
- Equivalence: =
- Inequality: != ^= <> ¬= (depends on platform)
SELECT name, salary, email FROM employees WHERE salary > 40000; SELECT name FROM customers WHERE customer_id < 6;
- Concatenate: ||
- Addition: +
- Subtraction: -
Basic PL/SQL Types
Scalar type (defined in package STANDARD): NUMBER, CHAR, VARCHAR2, BOOLEAN, BINARY_INTEGER, LONG\LONG RAW, DATE, TIMESTAMP(and its family including intervals)
Composite types (user-defined types): TABLE, RECORD, NESTED TABLE and VARRAY
LOB datatypes : used to store an unstructured large amount of data
%TYPE - anchored type variable declaration
The syntax for anchored type declarations is
<var_name> <obj>%type [not null][:= <init-val>];
name Books.title%type; /* name is defined as the same type as column 'title' of table Books */ commission number(5,2) := 12.5; x commission%type; /* x is defined as the same type as variable 'commission' */
- Anchored variables allow for the automatic synchronization of the type of anchored variable with the type of <obj> when there is a change to the <obj> type.
- Anchored types are evaluated at compile time, so recompile the program to reflect the change of <obj> type in the anchored variable.
A collection is an ordered group of elements, all of the same type. It is a general concept that encompasses lists, arrays, and other familiar datatypes. Each element has a unique subscript that determines its position in the collection.
--Define a PL/SQL record type representing a book: TYPE book_rec IS RECORD (title book.title%TYPE, author book.author_last_name%TYPE, year_published book.published_date%TYPE); --define a PL/SQL table containing entries of type book_rec: Type book_rec_tab IS TABLE OF book_rec%TYPE INDEX BY BINARY_INTEGER; my_book_rec book_rec%TYPE; my_book_rec_tab book_rec_tab%TYPE; ... my_book_rec := my_book_rec_tab(5); find_authors_books(my_book_rec.author); ...
There are many good reasons to use collections.
- Dramatically faster execution speed, thanks to transparent performance boosts including a new optimizing compiler, better integrated native compilation, and new datatypes that help out with number-crunching applications.
- The FORALL statement, made even more flexible and useful. For example, FORALL now supports nonconsecutive indexes.
- Regular expressions are available in PL/SQL in the form of three new functions (REGEXP_INSTR, REGEXP_REPLACE, and REGEXP_SUBSTR) and the REGEXP_LIKE operator for comparisons. (For more information, see "First Expressions" by Jonathan Gennick in this issue.)
- Collections, improved to include such things as collection comparison for equality and support for set operations on nested tables.
A function must return a value to the caller.
The syntax for a function is
CREATE [OR REPLACE] FUNCTION function_name [ (parameter [,parameter]) ] RETURN [return_datatype] IS [declaration_section] BEGIN executable_section return [return_value] [EXCEPTION exception_section] END [procedure_name];
CREATE OR REPLACE FUNCTION to_date_check_null(dateString IN VARCHAR2, dateFormat IN VARCHAR2) RETURN DATE IS BEGIN IF dateString IS NULL THEN return NULL; ELSE return to_date(dateString, dateFormat); END IF; END;
A procedure differs from a function in that it must not return a value to the caller.
The syntax for a procedure is:
CREATE [OR REPLACE] PROCEDURE procedure_name [ (parameter [,parameter]) ] IS [declaration_section] BEGIN executable_section [EXCEPTION exception_section] END [procedure_name];
When you create a procedure or function, you may define parameters. There are three types of parameters that can be declared:
- IN - The parameter can be referenced by the procedure or function. The value of the parameter can not be overwritten by the procedure or function.
- OUT - The parameter can not be referenced by the procedure or function, but the value of the parameter can be overwritten by the procedure or function.
- IN OUT - The parameter can be referenced by the procedure or function and the value of the parameter can be overwritten by the procedure or function.
Also you can declare a DEFAULT value;
CREATE [OR REPLACE] PROCEDURE procedure_name [ (parameter [IN|OUT|IN OUT] [DEFAULT value] [,parameter]) ]
The following is a simple example of a procedure:
/* purpose: shows the students in the course specified by courseId */ CREATE OR REPLACE Procedure GetNumberOfStudents ( courseId IN number, numberOfStudents OUT number ) IS /* although there are better ways to compute the number of students, this is a good opportunity to show a cursor in action */ cursor student_cur is select studentId, studentName from course where course.courseId = courseId; student_rec student_cur%ROWTYPE; BEGIN OPEN student_cur; LOOP FETCH student_cur INTO student_rec; EXIT WHEN student_cur%NOTFOUND; numberOfStudents := numberOfStudents + 1; END LOOP; CLOSE student_cur; EXCEPTION WHEN OTHERS THEN raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM); END GetNumberOfStudents;
DECLARE x NUMBER(4) := 0; BEGIN x := 1000; BEGIN x := x + 100; EXCEPTION WHEN OTHERS THEN x := x + 2; END; x := x + 10; dbms_output.put_line(x); EXCEPTION WHEN OTHERS THEN x := x + 3; END;
Passing Parameters to Stored Logic
There are three basic syntaxes for passing parameters to a stored procedure: positional notation, named notation and mixed notation.
In the following examples this procedure will be called each of the basic syntaxes for parameter passing:
CREATE OR REPLACE PROCEDURE create_customer ( p_name IN varchar2, p_id IN number, p_address IN varchar2, p_phone IN varchar2 ) IS BEGIN INSERT INTO customer ( name, id, address, phone ) VALUES ( p_name, p_id, p_address, p_phone ); END create_customer;
Specify the same parameters in the same order as they are declared in the procedure. This notation is compact, but if you specify the parameters (especially literals) in the wrong order, the bug can be hard to detect. You must change your code if the procedure's parameter list changes.
create_customer('James Whitfield', 33, '301 Anystreet', '251-222-3154');
Specify the name of each parameter along with its value. An arrow (=>) serves as the association operator. The order of the parameters is not significant. This notation is more verbose, but makes your code easier to read and maintain. You can sometimes avoid changing code if the procedure's parameter list changes, for example if the parameters are reordered or a new optional parameter is added. Named notation is a good practice to use for any code that calls someone else's API, or defines an API for someone else to use.
create_customer(p_address => '301 Anystreet', p_id => 33, p_name => 'James Whitfield', p_phone => '251-222-3154');
Specify the first parameters with positional notation, then switch to named notation for the last parameters. You can use this notation to call procedures that have some required parameters, followed by some optional parameters.
create_customer(v_name, v_id, p_address=> '301 Anystreet', p_phone => '251-222-3154');
CREATE TYPE object_row_type as OBJECT ( object_type VARCHAR(18), object_name VARCHAR(30) ); CREATE TYPE object_table_type as TABLE OF object_row_type; CREATE OR REPLACE FUNCTION get_all_objects RETURN object_table_type PIPELINED AS BEGIN FOR cur IN (SELECT * FROM all_objects) LOOP PIPE ROW(object_row_type(cur.object_type, cur.object_name)); END LOOP; RETURN; END; SELECT * FROM TABLE(get_all_objects);
- and: AND
- or: OR
- not: NOT
IF salary > 40000 AND salary <= 70000 THEN
IF [condition] THEN [statements] ELSIF [condition] THEN [statements} ELSIF [condition] THEN [statements} ELSIF [condition] THEN [statements} ELSIF [condition] THEN [statements} ELSIF [condition] THEN [statements} ELSIF [condition] THEN [statements} ELSIF [condition] THEN [statements} ELSE [statements} END IF;
- Strongly typed arrays, useful as in-memory tables
- Very simple example, the index is the key to accessing the array so there is no need to loop through the whole table unless you intend to use data from every line of the array.
- The index can also be a numeric value.
DECLARE -- Associative array indexed by string: -- Associative array type TYPE population IS TABLE OF NUMBER INDEX BY VARCHAR2(64); -- Associative array variable city_population population; i VARCHAR2(64); BEGIN -- Add new elements to associative array: city_population('Smallville') := 2000; city_population('Midland') := 750000; city_population('Megalopolis') := 1000000; -- Change value associated with key 'Smallville': city_population('Smallville') := 2001; -- Print associative array by looping through it: i := city_population.FIRST; WHILE i IS NOT NULL LOOP DBMS_OUTPUT.PUT_LINE ('Population of ' || i || ' is ' || TO_CHAR(city_population(i))); i := city_population.NEXT(i); END LOOP; -- Print selected value from a associative array: DBMS_OUTPUT.PUT_LINE('Selected value'); DBMS_OUTPUT.PUT_LINE('Population of END; / -- Printed results: Population of Megalopolis is 1000000 Population of Midland is 750000 Population of Smallville is 2001
- More complex example, using a record
DECLARE -- Record type TYPE apollo_rec IS RECORD ( commander VARCHAR2(100), launch DATE ); -- Associative array type TYPE apollo_type_arr IS TABLE OF apollo_rec INDEX BY VARCHAR2(100); -- Associative array variable apollo_arr apollo_type_arr; BEGIN apollo_arr('Apollo 11').commander := 'Neil Armstrong'; apollo_arr('Apollo 11').launch := TO_DATE('July 16, 1969','Month dd, yyyy'); apollo_arr('Apollo 12').commander := 'Pete Conrad'; apollo_arr('Apollo 12').launch := TO_DATE('November 14, 1969','Month dd, yyyy'); apollo_arr('Apollo 13').commander := 'James Lovell'; apollo_arr('Apollo 13').launch := TO_DATE('April 11, 1970','Month dd, yyyy'); apollo_arr('Apollo 14').commander := 'Alan Shepard'; apollo_arr('Apollo 14').launch := TO_DATE('January 31, 1971','Month dd, yyyy'); DBMS_OUTPUT.PUT_LINE(apollo_arr('Apollo 11').commander); DBMS_OUTPUT.PUT_LINE(apollo_arr('Apollo 11').launch); end; / -- Printed results: Neil Armstrong 16-JUL-69
* In SQL: :VARIABLE * In PL/SQL: V('VARIABLE') or NV('VARIABLE') * In text: &VARIABLE.