SQLite Like % and _

I can't figure out what the underscore character does in an SQLite like statement. The wildcard character, %, is probably the same as in most other SQL databases.

So, what does the _ character do?

It is standard SQL that in LIKE expressions:

• % matches any sequence of characters, including an empty one. It is equivalent to .* in a regular expression.

• _ matches a single character. It is equivalent to . in a regular expression.

• You can choose a character for escaping %, _ and itself itself with:

   ... WHERE expr LIKE 'a_b%c\\d\%\_' ESCAPE '\'
  

  This will match a×b×××c\d%_ or a×bc\d%_ but not abc\d%_ nor a×b×××cd%_.

Additionnally with SQLite you have the GLOB keyword which behaves exactly the same way, except that % becomes * and _ becomes ?.

The underscore is also the same as in most other SQL databases and matches any single character (i.e. it is the same as . in a regular expression). From the fine manual:

> An underscore ("_") in the LIKE pattern matches any single character in the string.

For example:

-- The '_' matches the single 'c'
sqlite> select 'pancakes' like 'pan_akes';
1
-- This would need '__' to match the 'ca', only one '_' fails.
sqlite> select 'pancakes' like 'pan_kes';
0
-- '___' also fails, one too many '_'.
sqlite> select 'pancakes' like 'pan___kes';
0

And just to make sure the results make sense: SQLite uses zero and one for booleans.

Addendum to @Benoit's answer:

The ESCAPE applies to the most recent LIKE expression, not all LIKE expressions. To escape all you must use ESCAPE multiple times, such as below.

WHERE foo LIKE '%bar^%%' ESCAPE '^' AND foo LIKE '%baz^_%' ESCAPE '^'

This predicate matches values of foo which contain bar%, or baz plus any character.

For the record, I use in XCode/Objective-C environment, '' doesn't work. Use anything else instead...

> C-style escapes using the backslash character are not supported because they are not standard SQL (https://www.sqlite.org/lang_expr.html)