Mysql
delete from table where x = ‘aaa’ limit 1;

Mssql
set rowcount 1;
delete from table where x = ‘aaa’;
set rowcount 0;

Self join is just like any other join, except that two instances of the same table will be joined in the query.

The difference is in the way tables are joined if there are no common records.

JOIN is same as INNER JOIN and means to only show records common to both tables. Whether the records are common is determined by the fields in join clause. For example:

FROM t1
JOIN t2 on t1.ID = t2.ID

means show only records where the same ID value exists in both tables.

LEFT JOIN is same as LEFT OUTER JOIN and means to show all records from left table (i.e. the one that precedes in SQL statement) regardless of the existance of matching records in the right table.

RIGHT JOIN is same as RIGHT OUTER JOIN and means opposite of LEFT JOIN, i.e. shows all records from the second (right) table and only matching records from first (left) table.

SELECT COUNT(*) FROM table_name;