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;

2146, 2146, 1

Simply, inner join gives both table’s common fields and outer join gives uncommon fields.

Inner join
SELECT CUSTOMERS.NAME, ORDERS.NAME
FROM CUSTOMERS
INNER JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID

Outer join
SELECT CUSTOMERS.NAME, ORDERS.NAME
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID

stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don’t need to keep re-issuing the entire query but can refer to the stored procedure. This provides better overall performance because the query has to be parsed only once, and less information needs to be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server. However, stored procedures of course do increase the load on the database server system, as more of the work is done on the server side and less on the client (application) side.

A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that stored procedure automatically deletes the corresponding customer from a customer table when all his transactions are deleted.

Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine the position to seek to in the middle of the data file without having to look at all the data. If a table has 1,000 rows, this is at least 100 times faster than reading sequentially. If you need to access most of the rows, it is faster to read sequentially, because this minimizes disk seeks.