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How does one escape special characters when writing SQL queries?

Escape quotes

Use two quotes for every one displayed. Examples:

SQL> SELECT 'Frank''s Oracle site' AS text FROM DUAL;

Franks's Oracle site


SQL> SELECT 'A ''quoted'' word.' AS text FROM DUAL;

A 'quoted' word.

Escape wildcard characters

The LIKE keyword allows for string searches. The '_' wild card character is used to match exactly one character, while '%' is used to match zero or more occurrences of any characters. These characters can be escaped in SQL. Examples:

SELECT name FROM emp 
   WHERE id LIKE '%/_%' ESCAPE '/';
SQL> SELECT 'A ''''double quoted'''' word.' AS text FROM DUAL;

A ''double quoted'' word.
SELECT name FROM emp 
   WHERE id LIKE '%\%%' ESCAPE '';

Escape ampersand (&) characters in SQL*Plus

When using SQL*Plus, the DEFINE setting can be changed to allow &'s (ampersands) to be used in text:

SELECT 'Lorel & Hardy' FROM dual;

Other methods:

Define an escape character:

SELECT '&abc' FROM dual;

Don't scan for substitution variables:

SELECT '&ABC' x FROM dual;

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