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The SQL NOT condition (sometimes called the NOT Operator) is used to negate a condition in the WHERE clause of a SELECT, INSERT, UPDATE, or DELETE statement.
The NOT LIKE operator in SQL is used on a column which is of type varchar . Usually, it is used with % which is used to represent any string value, including the null character \0 . The string we pass on to this operator is not case-sensitive.
The SQL EXCEPT operator is used to exclude like rows that are found in one query but not another. It returns rows that are unique to one result. To use the EXCEPT operator, both queries must return the same number of columns and those columns must be of compatible data types.
A null database field means that there is no value for a given record. It indicates the absence of a value. A blank database field means that there is a value for a given record, and this value is empty (for a string value) or 0 (for a numeric value).
What kind of field is this? The IN operator cannot be used with a single field, but is meant to be used in subqueries or with predefined lists:
-- subquery
SELECT a FROM x WHERE x.b NOT IN (SELECT b FROM y);
-- predefined list
SELECT a FROM x WHERE x.b NOT IN (1, 2, 3, 6);
If you are searching a string, go for the LIKE operator (but this will be slow):
-- Finds all rows where a does not contain "text"
SELECT * FROM x WHERE x.a NOT LIKE '%text%';
If you restrict it so that the string you are searching for has to start with the given string, it can use indices (if there is an index on that field) and be reasonably fast:
-- Finds all rows where a does not start with "text"
SELECT * FROM x WHERE x.a NOT LIKE 'text%';
SELECT * FROM table WHERE field1 NOT LIKE '%$x%'; (Make sure you escape $x properly beforehand to avoid SQL injection)
Edit: NOT IN does something a bit different - your question isn't totally clear so pick which one to use. LIKE 'xxx%' can use an index. LIKE '%xxx' or LIKE '%xxx%' can't.
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