SQL = vs. LIKE: When Should I Use Each Operator?

Differences and usage scenarios of = and LIKE operators in SQL

In SQL, both the = and LIKE operators are used to compare values, but there are significant differences in their behavior.

Detailed explanation of operators

= is not just a string comparison operator, but a general comparison operator suitable for numbers and strings. For strings, = compares the entire string as a unit.

LIKE is a specialized string operator that compares strings character by character. It allows matching various characters or character sequences using wildcard characters such as _ and %.

Impact of collation

= and LIKE both rely on the current collation to determine the result of the comparison. Collation refers to a set of rules and mechanisms for comparing strings within a given character set. Different collations can produce different results, even for seemingly simple comparisons.

Example description

Consider the following example:

<code class="language-sql">SELECT 'ä' LIKE 'ae' COLLATE latin1_german2_ci;
+-----------------------------------------+
| 'ä' LIKE 'ae' COLLATE latin1_german2_ci |
+-----------------------------------------+
|                                       0 |
+-----------------------------------------+

SELECT 'ä' = 'ae' COLLATE latin1_german2_ci;
+--------------------------------------+
| 'ä' = 'ae' COLLATE latin1_german2_ci |
+--------------------------------------+
|                                    1 |
+--------------------------------------+</code>

In this example, the = operator returns 1 (true), while the LIKE operator returns 0 (false). This is because the latin1_german2_ci collation treats lowercase "e" as the case-insensitive equivalent of lowercase "ä" with a diaeresis. However, the LIKE operator, which compares character by character, considers the two characters to be different.

Conclusion

= and LIKE are not interchangeable in SQL WHERE clauses, and there are significant differences in their behavior. = compares the entire string using the current collation, while LIKE compares the string character by character and may include wildcards.

Choose = or LIKE depending on the specific comparison needs. If you need to compare the entire string to find an exact match, = is a more appropriate choice. On the other hand, if the comparison involves wildcards or requires character-by-character analysis, LIKE is preferred. Careful consideration of these differences is critical to ensuring the accuracy and efficiency of your SQL queries.

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