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2.1.2.2 String Constants with C-Style Escapes

PostgreSQL also accepts “escape” string constants, which are an extension to the SQL standard. An escape string constant is specified by writing the letter E (upper or lower case) just before the opening single quote, e.g., E'foo'. (When continuing an escape string constant across lines, write E only before the first opening quote.) Within an escape string, a backslash character (\) begins a C-like backslash escape sequence, in which the combination of backslash and following character(s) represent a special byte value, as shown in Table 2-1.

Any other character following a backslash is taken literally. Thus, to include a backslash character, write two backslashes (\\). Also, a single quote can be included in an escape string by writing \', in addition to the normal way of ''.

It is your responsibility that the byte sequences you create, especially when using the octal or hexadecimal escapes, compose valid characters in the server character set encoding. When the server encoding is UTF-8, then the Unicode escapes or the alternative Unicode escape syntax, explained in section 2.1.2.3 String Constants with Unicode Escapes, should be used instead. (The alternative would be doing the UTF-8 encoding by hand and writing out the bytes, which would be very cumbersome.)

The Unicode escape syntax works fully only when the server encoding is UTF8. When other server encodings are used, only code points in the ASCII range (up to \u007F) can be specified. Both the 4-digit and the 8-digit form can be used to specify UTF-16 surrogate pairs to compose characters with code points larger than U+FFFF, although the availability of the 8-digit form technically makes this unnecessary. (When surrogate pairs are used when the server encoding is UTF8, they are first combined into a single code point that is then encoded in UTF-8.)

Caution: If the configuration parameter standard_conforming_strings is off, then PostgreSQL recognizes backslash escapes in both regular and escape string constants. This is for backward compatibility with the historical behavior, where backslash escapes were always recognized. Although standard_conforming_strings currently defaults to off, the default will change to on in a future release for improved standards compliance. Applications are therefore encouraged to migrate away from using backslash escapes. If you need to use a backslash escape to represent a special character, write the string constant with an E to be sure it will be handled the same way in future releases.

In addition to standard_conforming_strings, the configuration parameters escape_string_warning and backslash_quote govern treatment of backslashes in string constants.

The character with the code zero cannot be in a string constant.