mysql statement-level query optimization one
mysql statement-level query optimization two
One of mysql index analysis
The highest state of optimizing SQL is to return to the requirements. Only when the requirements are correctly understood can efficient SQL be written. Therefore, rewriting SQL is often an important means of optimizing SQL.
Although understanding the execution plan is an extremely important part of SQL optimization, if you cannot understand the requirements, write complex and tedious SQL statements with twists and turns, and optimize by analyzing the execution plan, you will often fall into the Helpless.
1. Join query type
1.1, SQL writing order
SELECT <select_list>
FROM
<left_table> <join_type> JOIN <right_table> ON <join_condition>
WHERE <where_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
ORDER BY <order_by_condition>
LIMIT <limit_number>
1.2, SQL execution order
FROM <left_table>
ON <join_condition>
<join_type> JOIN <right_table>
WHERE <where_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
SELECT
DISTINCT <select_list>
ORDER BY <order_by_condition>
LIMIT <limit_number>
1.3. Summary of SQL execution results
2 Diagram of JOIN query result set
2.1 LEFT JOIN ON
SELECT <select_list>
FROM tableA A
LEFT JOIN tableB B
ON A.key = B.key;
2.2 RIGHT JOIN ON
SELECT <select_list>
FROM tableA A
RIGHT JOIN tableB B
ON A.key = B.key;
2.3 INNER JOIN ON
join 默认为 inner join
SELECT <select_list>
FROM tableA A
INNER JOIN tableB B
ON A.key = B.key;
2.4 LEFT JOIN ON WHERE
SELECT <select_list>
FROM tableA A
LEFT JOIN tableB B
ON A.key = B.key
WHERE B.key IS NULL;
2.5 RIGHT JOIN ON WHERE
SELECT <select_list>
FROM tableA A
RIGHT JOIN tableB B
ON A.key = B.key
WHERE A.key IS NULL;
2.6 FULL OUTER JOIN ON
SELECT <select_list>
FROM tableA A
FULL OUTER JOIN tableB B
ON A.key = B.key
2.7 FULL OUTER JOIN ON WHERE
SELECT <select_list>
FROM tableA A
FULL OUTER JOIN tableB B
ON A.key = B.key
WHERE A.key IS NULL OR
B.key IS NULL
2.3. Create table SQL
2.4, 7 join instances
3. Index Introduction
4. Performance analysis
5. Index optimization
1. Performance decline SQL slow, long execution time, long waiting time