What Does \% and \\ Mean in a Sql Query?
I Know the Meaning of % and _ Wildcard Characters, but I Was Stuck in a Question Which Was Using the Two Additional Characters \% and \\, I Was Not Able to...
I know the meaning of % and _ wildcard characters ,but i was stuck in a question which was using the two additional characters \% and \\,i was not able to understand what these characters actually mean in the SQL query
SELECT productID
FROM productList
WHERE productName LIKE 'ab\%cd%'
and
SELECT productID
FROM productList
WHERE productName LIKE 'ab\\cd%'
are these two same things or different ??
3 Answers
Since % is a special character, you have to escape it with a \ to match a literal % symbol in your data. So, 'ab\%cd%' matches the letter a, followed by the letter b, followed by a % symbol, the letter c, the letter d, then any other text (because the last % is a wildcard).
Similarly, since \ is a special character used to create escape sequences, you have to escape it to match a literal \ in a pattern, so to match a single \ you have to encode it as \\.
I believe the best way to see the difference is by example.
To better understand it you will need knowledge about 3 things when using LIKE operator in SQL:
\is used to escape special characters to use them as normal chars%is used to match any number of characters (including 0)- special characters are
\and%so if you want to include them literally you need to escape them, so to check for them in text column you respectively need to use\\and\%.
Below is a table with words and true/false results for LIKE comparison with both patterns:
word | ab\%cd% | ab\\cd%
----------+---------+---------
ab\ | f | f -- this would match second pattern but there is no "cd" at the end
ab\cd | f | t -- \\ is escaped "\", and % matches none characters
ab\cdxzy | f | t -- \\ is escaped "\", and % matches character sequence "xzy"
abcd | f | f -- every string requires either "%" or "\" character after "ab"
ab%cd | t | f -- \% is escaped "%", and % matches none characters
ab%cdxzy | t | f -- \% is escaped "%", and % matches character sequence "xzy"
ab\%cd | f | f -- there is no pattern which matches both chars "\%" in sequence
ab%\cd | f | f -- same as above, but characters are "%\" in sequence
The
\%and\_sequences are used to search for literal instances of%and_in pattern-matching contexts where they would otherwise be interpreted as wildcard characters.
For \\ it searches for a single back slash \.
Ref: MySQL 8.0 Reference Manual, 9.1.1 String Literals, Table 9.1 Special Character Escape Sequences
James Sterling reports on renewable energy developments, climate policy, ecological conservation, and green tech innovations around the globe.
