DELETE statement

User's Guide

Part VI. SQL Anywhere Reference

Chapter 43. Watcom-SQL Statements
DELETE statement

Function

To delete rows from the database.

Syntax

     DELETE [FROM] [ owner.]table-name
          ...     [FROM table-list]
          ...     [WHERE search-condition]

Usage

Anywhere.

Permissions

Must have DELETE permission on the table.

Side effects

None.

Description

The DELETE statement deletes all the rows from the named table that satisfy the search condition. If no WHERE clause is specified, all rows from the named table are deleted.

The DELETE statement can be used on views provided the SELECT statement defining the view has only one table in the FROM clause and does not contain a GROUP BY clause, an aggregate function, or involve a UNION operation.

For a full description of the FROM clause and joins, see "FROM clause".

The optional second FROM clause in the DELETE statement allows rows to be deleted based on joins. If the second FROM clause is present, the WHERE clause qualifies the rows of this second FROM clause. Rows are deleted from the table name given in the first FROM clause.

Correlation name resolution

The following statement illustrates a potential ambiguity in table names in DELETE statements with two FROM clauses that use correlation names:

     DELETE
     FROM table_1
     FROM table_1 AS alias_1, table_2 AS alias_2
     WHERE ...

The table table_1 is identified without a correlation name in the first FROM clause, but with a correlation name in the second FROM clause. In this case, table_1 in the first clause is identified with alias_1 in the second clause---there is only one instance of table_1 in this statement.

This is an exception to the general rule that where a table is identified with a correlation name and without a correlation name in the same statement, two instances of the table are considered.

Consider the following example:

     DELETE
     FROM table_1
     FROM table_1 AS alias_1, table_1 AS alias_2
     WHERE ...

In this case, there are two instances of table_1 in the second from clause. In this case, there is no way of identifying which instance the first FROM clause should be identified with. The usual rules of correlation names apply, and table_1 in the first FROM clause is identified with neither instance in the second clause: there are three instances of table_1 in the statement.

Examples

Remove employee 105 from the database.

     DELETE
     FROM employee
     WHERE emp_id = 105

Remove all data prior to 1993 from the fin_data table.

     DELETE
     FROM fin_data
     WHERE year < 1993

Remove all names from the contact table if they are already present in the customer table.

     DELETE
     FROM contact
     FROM contact, customer
     WHERE contact.last_name = customer.lname
     AND contact.first_name = customer.fname