OVERLAY()

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OVERLAY()

OVERLAY() — Returns a string overwriting a portion of the original string with the specified replacement.

Synopsis

OVERLAY( string PLACING replacement-string FROM position [FOR length] )

Description

The OVERLAY() function overwrites a portion of the original string with the replacement string and returns the result. The replacement starts at the specified position in the original string and either replaces the characters one-for-one for the length of the replacement string or, if a FOR length is specified, replaces the specified number of characters.

For example, if the original string is 12 characters in length, the replacement string is 3 characters in length and starts at position 4, and the FOR clause is left off, the resulting string consists of the first 3 characters of the original string, the replacement string, and the last 6 characters of the original string:

OVERLAY('abcdefghijkl' PLACING 'XYZ' FROM 4) = 'abcXYZghijkl'

If the FOR clause is included specifying that the replacement string replaces 6 characters, the result is the first 3 characters of the original string, the replacement string, and the last 3 characters of the original string:

OVERLAY('abcdefghijkl' PLACING 'XYZ' FROM 4 FOR 6) = 'abcXYZjkl'

If the combination of the starting position and the replacement length exceed the length of the original string, the resulting output is extended as necessary to include all of the replacement string:

OVERLAY('abcdef' PLACING 'XYZ' FROM 5) = 'abcdXYZ'

If the starting position is greater than the length of the original string, the replacement string is appended to the original string:

OVERLAY('abcdef' PLACING 'XYZ' FROM 20) = 'abcdefXYZ'

Similarly, if the combination of the starting position and the FOR length is greater than the length of the original string, the replacement string simply overwrites the remainder of the original string:

OVERLAY('abcdef' PLACING 'XYZ' FROM 2 FOR 20) = 'aXYZ'

The starting position and length must be specified as non-negative integers. The starting position must be greater than zero and the length can be zero or greater.

Example

The following example uses the OVERLAY function to redact part of a name.

SELECT OVERLAY( fullname PLACING '****' FROM 2 
                FOR CHAR_LENGTH(fullname)-2
       ) FROM users ORDER BY fullname;
>