B.3.4.1 Case Sensitivity in String Searches

For nonbinary strings (CHAR, VARCHAR, TEXT), string searches use the collation of the comparison operands. For binary strings (BINARY, VARBINARY, BLOB), comparisons use the numeric values of the bytes in the operands; this means that for alphabetic characters, comparisons are case-sensitive.

A comparison between a nonbinary string and binary string is treated as a comparison of binary strings.

Simple comparison operations (>=, >, =, <, <=, sorting, and grouping) are based on each character's “sort value.” Characters with the same sort value are treated as the same character. For example, if e and é have the same sort value in a given collation, they compare as equal.

The default character set and collation are latin1 and latin1_swedish_ci, so nonbinary string comparisons are case-insensitive by default. This means that if you search with col_name LIKE 'a%', you get all column values that start with A or a. To make this search case-sensitive, make sure that one of the operands has a case-sensitive or binary collation. For example, if you are comparing a column and a string that both have the latin1 character set, you can use the COLLATE operator to cause either operand to have the latin1_general_cs or latin1_bin collation:

col_name COLLATE latin1_general_cs LIKE 'a%'
col_name LIKE 'a%' COLLATE latin1_general_cs
col_name COLLATE latin1_bin LIKE 'a%'
col_name LIKE 'a%' COLLATE latin1_bin

If you want a column always to be treated in case-sensitive fashion, declare it with a case-sensitive or binary collation. See Section 13.1.18, “CREATE TABLE Statement”.

To cause a case-sensitive comparison of nonbinary strings to be case-insensitive, use COLLATE to name a case-insensitive collation. The strings in the following example normally are case-sensitive, but COLLATE changes the comparison to be case-insensitive:

mysql> SET @s1 = 'MySQL' COLLATE latin1_bin,
    ->     @s2 = 'mysql' COLLATE latin1_bin;
mysql> SELECT @s1 = @s2;
+-----------+
| @s1 = @s2 |
+-----------+
|         0 |
+-----------+
mysql> SELECT @s1 COLLATE latin1_swedish_ci = @s2;
+-------------------------------------+
| @s1 COLLATE latin1_swedish_ci = @s2 |
+-------------------------------------+
|                                   1 |
+-------------------------------------+

A binary string is case-sensitive in comparisons. To compare the string as case-insensitive, convert it to a nonbinary string and use COLLATE to name a case-insensitive collation:

mysql> SET @s = BINARY 'MySQL';
mysql> SELECT @s = 'mysql';
+--------------+
| @s = 'mysql' |
+--------------+
|            0 |
+--------------+
mysql> SELECT CONVERT(@s USING latin1) COLLATE latin1_swedish_ci = 'mysql';
+--------------------------------------------------------------+
| CONVERT(@s USING latin1) COLLATE latin1_swedish_ci = 'mysql' |
+--------------------------------------------------------------+
|                                                            1 |
+--------------------------------------------------------------+

To determine whether a value compares as a nonbinary or binary string, use the COLLATION() function. This example shows that VERSION() returns a string that has a case-insensitive collation, so comparisons are case-insensitive:

mysql> SELECT COLLATION(VERSION());
+----------------------+
| COLLATION(VERSION()) |
+----------------------+
| utf8_general_ci      |
+----------------------+

For binary strings, the collation value is binary, so comparisons are case-sensitive. One context in which you may see binary is for compression functions, which return binary strings as a general rule:

mysql> SELECT COLLATION(COMPRESS('x'));
+--------------------------+
| COLLATION(COMPRESS('x')) |
+--------------------------+
| binary                   |
+--------------------------+

To check the sort value of a string, the WEIGHT_STRING() may be helpful. See Section 12.8, “String Functions and Operators”.