8/11/2023 0 Comments Change data type in postgresqlNote that trailing spaces are semantically significant in character varying and text values, and when using pattern matching, that is LIKE and regular expressions. Trailing spaces are removed when converting a character value to one of the other string types. In collations where whitespace is significant, this behavior can produce unexpected results for example SELECT 'a '::CHAR(2) collate "C" < E'a\n'::CHAR(2) returns true, even though C locale would consider a space to be greater than a newline. However, trailing spaces are treated as semantically insignificant and disregarded when comparing two values of type character. Values of type character are physically padded with spaces to the specified width n, and are stored and displayed that way. Although the type text is not in the SQL standard, several other SQL database management systems have it as well. In addition, PostgreSQL provides the text type, which stores strings of any length. If character varying is used without length specifier, the type accepts strings of any size. character without length specifier is equivalent to character(1). If specified, the length must be greater than zero and cannot exceed 10485760. The notations varchar( n) and char( n) are aliases for character varying( n) and character( n), respectively. (This too is required by the SQL standard.) If one explicitly casts a value to character varying( n) or character( n), then an over-length value will be truncated to n characters without raising an error. (This somewhat bizarre exception is required by the SQL standard.) If the string to be stored is shorter than the declared length, values of type character will be space-padded values of type character varying will simply store the shorter string. An attempt to store a longer string into a column of these types will result in an error, unless the excess characters are all spaces, in which case the string will be truncated to the maximum length. Both of these types can store strings up to n characters (not bytes) in length. SQL defines two primary character types: character varying( n) and character( n), where n is a positive integer. Table 8.4 shows the general-purpose character types available in PostgreSQL.
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