Difference between revisions of "Mysql query syntax and examples"

Revision as of 20:57, 28 August 2017

OVERVIEW

This page to hold Ted's notes and 2017 studies of MYSQL syntax and practical examples.

MYSQL Keywords and Clauses

Excerpt from MYSQL documentation at [https://dev.mysql.com/doc/refman/5.7/en/join.html MYSQL 5.7 Reference Manual, JOIN syntax . . .

" The conditional_expr used with ON is any conditional expression of the form that can be used in a WHERE clause. Generally, the ON clause serves for conditions that specify how to join tables, and the WHERE clause restricts which rows to include in the result set. "

EXAMPLES

MYSQL's IN clause, useful to combine OR statements in queries and useful to express subqueries. The following example query shows how to, in OpenCart's database tables, change the status of products which associated with a particular category. Product statae live in one table, and numeric identifiers (ids) associated with products live in another table. MYSQL's IN clause allows us to update product statae in one table, for those prooducts whose ids match conditions in another table. This is a very simple use of MYSQL IN clause:

Code example x - MYSQL IN clause:

    mysql> update oc_product as t1 set t1.status = 0 where t1.product_id in (select t2.product_id from oc_product_to_category as t2 where t2.category_id = 60);
    Query OK, 18 rows affected (0.00 sec)
    Rows matched: 18  Changed: 18  Warnings: 0

    mysql> update oc_product as t1 set t1.status = 0 where t1.product_id in (select t2.product_id from oc_product_to_category as t2 where t2.category_id = 64);
    Query OK, 6 rows affected (0.00 sec)
    Rows matched: 6  Changed: 6  Warnings: 0

mysql>

REFERENCES

• MYSQL JOIN syntax