- •Contents
- •Send Us Your Comments
- •Preface
- •What’s New in SQL Reference?
- •1 Introduction to Oracle SQL
- •History of SQL
- •SQL Standards
- •Embedded SQL
- •Lexical Conventions
- •Tools Support
- •2 Basic Elements of Oracle SQL
- •Datatypes
- •Oracle Built-in Datatypes
- •ANSI, DB2, and SQL/DS Datatypes
- •Oracle-Supplied Types
- •"Any" Types
- •XML Types
- •Spatial Type
- •Media Types
- •Datatype Comparison Rules
- •Data Conversion
- •Literals
- •Text Literals
- •Integer Literals
- •Number Literals
- •Interval Literals
- •Format Models
- •Number Format Models
- •Date Format Models
- •String-to-Date Conversion Rules
- •XML Format Model
- •Nulls
- •Nulls in SQL Functions
- •Nulls with Comparison Conditions
- •Nulls in Conditions
- •Pseudocolumns
- •CURRVAL and NEXTVAL
- •LEVEL
- •ROWID
- •ROWNUM
- •XMLDATA
- •Comments
- •Comments Within SQL Statements
- •Comments on Schema Objects
- •Hints
- •Database Objects
- •Schema Objects
- •Nonschema Objects
- •Parts of Schema Objects
- •Schema Object Names and Qualifiers
- •Schema Object Naming Rules
- •Schema Object Naming Examples
- •Schema Object Naming Guidelines
- •Syntax for Schema Objects and Parts in SQL Statements
- •How Oracle Resolves Schema Object References
- •Referring to Objects in Other Schemas
- •Referring to Objects in Remote Databases
- •Referencing Object Type Attributes and Methods
- •3 Operators
- •About SQL Operators
- •Unary and Binary Operators
- •Operator Precedence
- •Arithmetic Operators
- •Concatenation Operator
- •Set Operators
- •4 Expressions
- •About SQL Expressions
- •Simple Expressions
- •Compound Expressions
- •CASE Expressions
- •CURSOR Expressions
- •Datetime Expressions
- •Function Expressions
- •INTERVAL Expressions
- •Object Access Expressions
- •Scalar Subquery Expressions
- •Type Constructor Expressions
- •Variable Expressions
- •Expression Lists
- •5 Conditions
- •About SQL Conditions
- •Condition Precedence
- •Comparison Conditions
- •Simple Comparison Conditions
- •Group Comparison Conditions
- •Logical Conditions
- •Membership Conditions
- •Range Conditions
- •Null Conditions
- •EQUALS_PATH
- •EXISTS Conditions
- •LIKE Conditions
- •IS OF type Conditions
- •UNDER_PATH
- •Compound Conditions
- •6 Functions
- •SQL Functions
- •Single-Row Functions
- •Aggregate Functions
- •Analytic Functions
- •Object Reference Functions
- •Alphabetical Listing of SQL Functions
- •ACOS
- •ADD_MONTHS
- •ASCII
- •ASCIISTR
- •ASIN
- •ATAN
- •ATAN2
- •BFILENAME
- •BITAND
- •CAST
- •CEIL
- •CHARTOROWID
- •COALESCE
- •COMPOSE
- •CONCAT
- •CONVERT
- •CORR
- •COSH
- •COUNT
- •COVAR_POP
- •COVAR_SAMP
- •CUME_DIST
- •CURRENT_DATE
- •CURRENT_TIMESTAMP
- •DBTIMEZONE
- •DECODE
- •DECOMPOSE
- •DENSE_RANK
- •DEPTH
- •DEREF
- •DUMP
- •EMPTY_BLOB, EMPTY_CLOB
- •EXISTSNODE
- •EXTRACT (datetime)
- •EXTRACT (XML)
- •EXTRACTVALUE
- •FIRST
- •FIRST_VALUE
- •FLOOR
- •FROM_TZ
- •GREATEST
- •GROUP_ID
- •GROUPING
- •GROUPING_ID
- •HEXTORAW
- •INITCAP
- •INSTR
- •LAST
- •LAST_DAY
- •LAST_VALUE
- •LEAD
- •LEAST
- •LENGTH
- •LOCALTIMESTAMP
- •LOWER
- •LPAD
- •LTRIM
- •MAKE_REF
- •MONTHS_BETWEEN
- •NCHR
- •NEW_TIME
- •NEXT_DAY
- •NLS_CHARSET_DECL_LEN
- •NLS_CHARSET_ID
- •NLS_CHARSET_NAME
- •NLS_INITCAP
- •NLS_LOWER
- •NLSSORT
- •NLS_UPPER
- •NTILE
- •NULLIF
- •NUMTODSINTERVAL
- •NUMTOYMINTERVAL
- •PATH
- •PERCENT_RANK
- •PERCENTILE_CONT
- •PERCENTILE_DISC
- •POWER
- •RANK
- •RATIO_TO_REPORT
- •RAWTOHEX
- •RAWTONHEX
- •REFTOHEX
- •REGR_ (Linear Regression) Functions
- •REPLACE
- •ROUND (number)
- •ROUND (date)
- •ROW_NUMBER
- •ROWIDTOCHAR
- •ROWIDTONCHAR
- •RPAD
- •RTRIM
- •SESSIONTIMEZONE
- •SIGN
- •SINH
- •SOUNDEX
- •SQRT
- •STDDEV
- •STDDEV_POP
- •STDDEV_SAMP
- •SUBSTR
- •SYS_CONNECT_BY_PATH
- •SYS_CONTEXT
- •SYS_DBURIGEN
- •SYS_EXTRACT_UTC
- •SYS_GUID
- •SYS_TYPEID
- •SYS_XMLAGG
- •SYS_XMLGEN
- •SYSDATE
- •SYSTIMESTAMP
- •TANH
- •TO_CHAR (character)
- •TO_CHAR (datetime)
- •TO_CHAR (number)
- •TO_CLOB
- •TO_DATE
- •TO_DSINTERVAL
- •TO_MULTI_BYTE
- •TO_NCHAR (character)
- •TO_NCHAR (datetime)
- •TO_NCHAR (number)
- •TO_NCLOB
- •TO_NUMBER
- •TO_SINGLE_BYTE
- •TO_TIMESTAMP
- •TO_TIMESTAMP_TZ
- •TO_YMINTERVAL
- •TRANSLATE
- •TRANSLATE ... USING
- •TREAT
- •TRIM
- •TRUNC (number)
- •TRUNC (date)
- •TZ_OFFSET
- •UNISTR
- •UPDATEXML
- •UPPER
- •USER
- •USERENV
- •VALUE
- •VAR_SAMP
- •VARIANCE
- •VSIZE
- •WIDTH_BUCKET
- •XMLAGG
- •XMLCOLATTVAL
- •XMLCONCAT
- •XMLELEMENT
- •XMLFOREST
- •XMLSEQUENCE
- •XMLTRANSFORM
- •ROUND and TRUNC Date Functions
- •User-Defined Functions
- •Prerequisites
- •Name Precedence
- •7 Common SQL DDL Clauses
- •allocate_extent_clause
- •constraints
- •deallocate_unused_clause
- •file_specification
- •logging_clause
- •parallel_clause
- •physical_attributes_clause
- •storage_clause
- •8 SQL Queries and Subqueries
- •About Queries and Subqueries
- •Creating Simple Queries
- •Hierarchical Queries
- •The UNION [ALL], INTERSECT, MINUS Operators
- •Sorting Query Results
- •Joins
- •Using Subqueries
- •Unnesting of Nested Subqueries
- •Selecting from the DUAL Table
- •Distributed Queries
- •9 SQL Statements: ALTER CLUSTER to ALTER SEQUENCE
- •Types of SQL Statements
- •Organization of SQL Statements
- •ALTER CLUSTER
- •ALTER DATABASE
- •ALTER DIMENSION
- •ALTER FUNCTION
- •ALTER INDEX
- •ALTER INDEXTYPE
- •ALTER JAVA
- •ALTER MATERIALIZED VIEW
- •ALTER MATERIALIZED VIEW LOG
- •ALTER OPERATOR
- •ALTER OUTLINE
- •ALTER PACKAGE
- •ALTER PROCEDURE
- •ALTER PROFILE
- •ALTER RESOURCE COST
- •ALTER ROLE
- •ALTER ROLLBACK SEGMENT
- •ALTER SEQUENCE
- •10 SQL Statements: ALTER SESSION to ALTER SYSTEM
- •ALTER SESSION
- •ALTER SYSTEM
- •ALTER TABLE
- •ALTER TABLESPACE
- •ALTER TRIGGER
- •ALTER TYPE
- •ALTER USER
- •ALTER VIEW
- •ANALYZE
- •ASSOCIATE STATISTICS
- •AUDIT
- •CALL
- •COMMENT
- •COMMIT
- •13 SQL Statements: CREATE CLUSTER to CREATE JAVA
- •CREATE CLUSTER
- •CREATE CONTEXT
- •CREATE CONTROLFILE
- •CREATE DATABASE
- •CREATE DATABASE LINK
- •CREATE DIMENSION
- •CREATE DIRECTORY
- •CREATE FUNCTION
- •CREATE INDEX
- •CREATE INDEXTYPE
- •CREATE JAVA
- •14 SQL Statements: CREATE LIBRARY to CREATE SPFILE
- •CREATE LIBRARY
- •CREATE MATERIALIZED VIEW
- •CREATE MATERIALIZED VIEW LOG
- •CREATE OPERATOR
- •CREATE OUTLINE
- •CREATE PACKAGE
- •CREATE PACKAGE BODY
- •CREATE PFILE
- •CREATE PROCEDURE
- •CREATE PROFILE
- •CREATE ROLE
- •CREATE ROLLBACK SEGMENT
- •CREATE SCHEMA
- •CREATE SEQUENCE
- •CREATE SPFILE
- •15 SQL Statements: CREATE SYNONYM to CREATE TRIGGER
- •CREATE SYNONYM
- •CREATE TABLE
- •CREATE TABLESPACE
- •CREATE TEMPORARY TABLESPACE
- •CREATE TRIGGER
- •CREATE TYPE
- •CREATE TYPE BODY
- •CREATE USER
- •CREATE VIEW
- •DELETE
- •DISASSOCIATE STATISTICS
- •DROP CLUSTER
- •DROP CONTEXT
- •DROP DATABASE LINK
- •DROP DIMENSION
- •DROP DIRECTORY
- •DROP FUNCTION
- •DROP INDEX
- •DROP INDEXTYPE
- •DROP JAVA
- •DROP LIBRARY
- •DROP MATERIALIZED VIEW
- •DROP MATERIALIZED VIEW LOG
- •DROP OPERATOR
- •DROP OUTLINE
- •DROP PACKAGE
- •DROP PROCEDURE
- •DROP PROFILE
- •DROP ROLE
- •DROP ROLLBACK SEGMENT
- •17 SQL Statements: DROP SEQUENCE to ROLLBACK
- •DROP SEQUENCE
- •DROP SYNONYM
- •DROP TABLE
- •DROP TABLESPACE
- •DROP TRIGGER
- •DROP TYPE
- •DROP TYPE BODY
- •DROP USER
- •DROP VIEW
- •EXPLAIN PLAN
- •GRANT
- •INSERT
- •LOCK TABLE
- •MERGE
- •NOAUDIT
- •RENAME
- •REVOKE
- •ROLLBACK
- •18 SQL Statements: SAVEPOINT to UPDATE
- •SAVEPOINT
- •SELECT
- •SET CONSTRAINT[S]
- •SET ROLE
- •SET TRANSACTION
- •TRUNCATE
- •UPDATE
- •Required Keywords and Parameters
- •Optional Keywords and Parameters
- •Syntax Loops
- •Multipart Diagrams
- •Database Objects
- •ANSI Standards
- •ISO Standards
- •Oracle Compliance
- •FIPS Compliance
- •Oracle Extensions to Standard SQL
- •Character Set Support
- •Using Extensible Indexing
- •Using XML in SQL Statements
- •Index
LOCK TABLE
LOCK TABLE
Purpose
Use the LOCK TABLE statement to lock one or more tables (or table partitions or subpartitions) in a specified mode. This lock manually overrides automatic locking and permits or denies access to a table or view by other users for the duration of your operation.
Some forms of locks can be placed on the same table at the same time. Other locks allow only one lock for a table.
A locked table remains locked until you either commit your transaction or roll it back, either entirely or to a savepoint before you locked the table.
A lock never prevents other users from querying the table. A query never places a lock on a table. Readers never block writers and writers never block readers.
See Also:
■Oracle9i Database Concepts for a complete description of the interaction of lock modes
■
■
■
COMMIT on page 12-75
ROLLBACK on page 17-99
SAVEPOINT on page 18-2
Prerequisites
The table or view must be in your own schema or you must have the LOCK ANY TABLE system privilege, or you must have any object privilege on the table or view.
SQL Statements: DROP SEQUENCE to ROLLBACK 17-73
LOCK TABLE
Syntax
lock_table::=
LOCK 
TABLE
,
PARTITION 
( 
partition 
)
SUBPARTITION 
( 
subpartition 
)
|
schema |
. |
table |
@ |
dblink |
|
|
|
view |
|
|
|
|
|
NOWAIT |
|
|
IN |
lockmode |
MODE |
|
; |
|
Semantics
schema
Specify the schema containing the table or view. If you omit schema, then Oracle assumes the table or view is in your own schema.
table / view
Specify the name of the table to be locked.
If you specify view, then Oracle locks the view’s base tables.
If you specify PARTITION (partition) or SUBPARTITION (subpartition), then Oracle first acquires an implicit lock on the table. The table lock is the same as the lock you specify for partition or subpartition, with two exceptions:
■If you specify a SHARE lock for the subpartition, then Oracle acquires an implicit ROW SHARE lock on the table.
■If you specify an EXCLUSIVE lock for the subpartition, then Oracle acquires an implicit ROW EXCLUSIVE lock on the table.
If you specify PARTITION and table is composite-partitioned, then Oracle acquires locks on all the subpartitions of partition.
Restriction on Locking Tables If table is part of a hierarchy, then it must be the root of the hierarchy.
17-74 Oracle9i SQL Reference
LOCK TABLE
dblink
Specify a database link to a remote Oracle database where the table or view is located. You can lock tables and views on a remote database only if you are using Oracle’s distributed functionality. All tables locked by a LOCK TABLE statement must be on the same database.
If you omit dblink, then Oracle assumes the table or view is on the local database.
See Also: "Referring to Objects in Remote Databases" on page 2-118 for information on specifying database links
lockmode Clause
Specify one of the following modes:
ROW SHARE ROW SHARE permits concurrent access to the locked table, but prohibits users from locking the entire table for exclusive access. ROW SHARE is synonymous with SHARE UPDATE, which is included for compatibility with earlier versions of Oracle.
ROW EXCLUSIVE ROW EXCLUSIVE is the same as ROW SHARE, but also prohibits locking in SHARE mode. ROW EXCLUSIVE locks are automatically obtained when updating, inserting, or deleting.
SHARE UPDATE See ROW SHARE.
SHARE SHARE permits concurrent queries but prohibits updates to the locked table.
SHARE ROW EXCLUSIVE SHARE ROW EXCLUSIVE is used to look at a whole table and to allow others to look at rows in the table but to prohibit others from locking the table in SHARE mode or updating rows.
EXCLUSIVE EXCLUSIVE permits queries on the locked table but prohibits any other activity on it.
NOWAIT
Specify NOWAIT if you want Oracle to return control to you immediately if the specified table (or specified partition or subpartition) is already locked by another user. In this case, Oracle returns a message indicating that the table, partition, or subpartition is already locked by another user.
SQL Statements: DROP SEQUENCE to ROLLBACK 17-75
LOCK TABLE
If you omit this clause, then Oracle waits until the table is available, locks it, and returns control to you.
Examples
Locking a Table: Example The following statement locks the employees table in exclusive mode, but does not wait if another user already has locked the table:
LOCK TABLE employees
IN EXCLUSIVE MODE
NOWAIT;
The following statement locks the remote employees table that is accessible through the database link remote:
LOCK TABLE employees@remote
IN SHARE MODE;
17-76 Oracle9i SQL Reference