Oracle Database/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 frequently uses 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 throughout the net. We developed this resource to make it easier for programmers and DBAs to find most of the basics in one place. Topics beyond the scope of a "cheatsheet" generally provide a link to further research.

Other Oracle References
 * Oracle XML Reference—the XML reference is still in its infancy, but is coming along nicely.

SELECT
The SELECT statement is used to retrieve rows selected from one or more tables, object tables, views, object views, or materialized views.

SELECT INTO
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 raises the  built-in exception. If your query returns more than one row, Oracle raises the exception.

INSERT
The INSERT statement adds one or more new rows of data to a database table.

insert using the VALUES keyword

insert using a SELECT statement

DELETE
The DELETE statement is used to delete rows in a table.

deletes rows that match the criteria

UPDATE
The UPDATE statement is used to update rows in a table.

updates the entire column of that table

updates the specific record of the table eg:

updates the column invoice as paid when paid column has more than zero.

SEQUENCES
Sequences are database objects that multiple users can use to generate unique integers. The sequence generator generates sequential numbers, which can help automatically generate unique primary keys, and coordinate keys across multiple rows or tables.

CREATE SEQUENCE
The syntax for a sequence is:

For example:

ALTER SEQUENCE
Increment a sequence by a certain amount:

Change the maximum value of a sequence:

Set the sequence to cycle or not cycle:

Configure the sequence to cache a value:

Set whether or not to return the values in order

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.

Length
Length returns an integer representing the length of a given string. It can be referred to as: length b, length c, length 2, and length 4.

length( string1 );

SELECT length('hello world') FROM dual; this returns 11, since the argument is made up of 11 characters including the space

SELECT lengthb('hello world') FROM dual; SELECT lengthc('hello world') FROM dual; SELECT length2('hello world') FROM dual; SELECT length4('hello world') FROM dual; these also return 11, since the functions called are equivalent

Instr
Instr (in string) returns an integer that 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. An unsuccessful search returns 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
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
Substr (substring) 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])
 * 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")


 * returns "cheatsheet" since "c" is in the 15th position in the string and "t" is the last character in the string.


 * returns "cheat" since "c" is the 10th character in the string, counting from the end of the string with "t" as position 1.

Trim
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"

Create table
The syntax to create a table is: CREATE TABLE [table name] ( [column name] [datatype], ... ); For example:

Add column
The syntax to add a column is: ALTER TABLE [table name] ADD ( [column name] [datatype], ... ); For example:

Modify column
The syntax to modify a column is: ALTER TABLE [table name] MODIFY ( [column name] [new datatype] );

ALTER table syntax and examples:

For example:

Drop column
The syntax to drop a column is: ALTER TABLE [table name] DROP COLUMN [column name]; For example:

Displaying constraints
The following statement shows all constraints in the system:

Selecting referential constraints
The following statement shows all referential constraints (foreign keys) with both source and destination table/column couples:

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] ); For example:

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) );

For example:

Adding unique constraints
The syntax for a unique constraint is:

ALTER TABLE [table name] ADD CONSTRAINT [constraint name] UNIQUE( [column name] ) USING INDEX [index name];

For example:

Adding foreign constraints
The syntax for a foregin constraint is:

ALTER TABLE [table name] ADD CONSTRAINT [constraint name] FOREIGN KEY (column,...) REFERENCES table [(column,...)] [ON DELETE {CASCADE | SET NULL}]

For example:

Deleting constraints
The syntax for dropping (removing) a constraint is:

ALTER TABLE [table name] DROP CONSTRAINT [constraint name];

For example:

INDEXES
An index is a method that retrieves records with greater efficiency. An index creates an entry for each value that appears in the indexed columns. By default, Oracle creates 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.

For example: 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: The following collects statistics upon creation of the index:

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 that creates a function-based index is:

CREATE [UNIQUE] INDEX index_name ON table_name (function1, function2, . function_n) [ COMPUTE STATISTICS ];

For example: 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:

Rename an Index
The syntax for renaming an index is:

ALTER INDEX index_name RENAME TO new_index_name;

For example: 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;

For example: 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;

For example: In this example, the customer_idx is dropped.

Creating a user
The syntax for creating a user is:

CREATE USER username IDENTIFIED BY password;

For example:

CREATE USER brian IDENTIFIED BY brianpass;

Granting privileges
The syntax for granting privileges is:

GRANT privilege TO user;

For example:

GRANT dba TO brian;

Change password
The syntax for changing user password is:

ALTER USER username IDENTIFIED BY password;

For example:

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.

Import 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:

imp KEYWORD=value

There are number of parameters you can use for keywords.

To view all the keywords:

imp HELP=yes

An example:

imp brian/brianpassword FILE=mydump.dmp FULL=yes

Arithmetic operators

 * Addition: +
 * Subtraction: -
 * Multiplication: *
 * Division: /
 * Power (PL/SQL only): **

Examples
gives all employees from customer id 5 a 5% raise UPDATE employee SET salary = salary * 1.05 WHERE customer_id = 5;

determines the after tax wage for all employees SELECT wage – tax FROM employee;

Comparison operators

 * Greater Than: >
 * Greater Than or Equal To: >=
 * Less Than: <
 * Less Than or Equal to: <=
 * Equivalence: =
 * Inequality: != ^=  <>  ¬= (depends on platform)

Examples
SELECT name, salary, email FROM employees WHERE salary > 40000;

SELECT name FROM customers WHERE customer_id < 6;

String operators
create or replace procedure addtest( a in varchar2(100), b in varchar2(100), c out varchar2(200) ) IS begin C:=concat(a,'-',b);
 * Concatenate: ||

Date operators

 * 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  %type [not null][:= ];

For example 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' */

Note:   Anchored variables allow for the automatic synchronization of the type of anchored variable with the type of when there is a change to the type.  Anchored types are evaluated at compile time, so recompile the program to reflect the change of type in the anchored variable. 

Collections
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 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.


 * Collections, improved to include such things as collection comparison for equality and support for set operations on nested tables.

Functions
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 [function_name];

For example: 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;

Procedures
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.</li> <li> 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.</li> <li> 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.</li> </ol>

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;

anonymous block
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.

The following examples call this procedure for 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;

Positional notation
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');

Named notation
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');

Mixed notation
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');

Table functions
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);

Conditional Operators

 * and: AND
 * or: OR
 * not: NOT

Example
IF salary > 40000 AND salary <= 70000 THEN ELSE IF salary>70000 AND salary<=100000 THEN ELSE

If/then/else
IF [condition] THEN [statements] ELSEIF [condition] THEN [statements} ELSEIF [condition] THEN [statements} ELSEIF [condition] THEN [statements} ELSEIF [condition] THEN [statements} ELSEIF [condition] THEN [statements} ELSEIF [condition] THEN [statements} ELSEIF [condition] THEN [statements} ELSE [statements} END IF;

Associative arrays

 * Strongly typed arrays, useful as in-memory tables

Example

 * 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.


 * More complex example, using a record

APEX
aka APEX, is a web-based software development environment that runs on an Oracle database.

String substitution

 * In SQL: :VARIABLE
 * In PL/SQL: V('VARIABLE') or NV('VARIABLE')
 * In text: &VARIABLE.