MySQL-multi-table query-summary 1

Table of contents

inner join

outer join

subqueries (nested queries)

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inner join

• The inner join query is the intersection part between tables
• implicit inner join
  • select field list from table 1, table 2 where condition....;
• Show Inner Links
  • select field list from table 1 [ inner ] join table 2 on condition....;

outer join

• Left outer join (general use)
  • select field list from table 1 left join table 2 on condition...;
• right outer join
  • select field list from table 1 right join table 2 on condition...;

subqueries (nested queries)

• scalar subqueries
  • The result returned by the subquery is a single value
• column query
  • The result returned by the subquery is one column but can be multiple rows
• row subquery
  • The result returned by the subquery is one row but can be multiple columns
• table subquery
  • The result returned by the subquery is multiple rows and multiple columns (usually as a temporary table)
• ps: Since the use of subqueries will query the data in the table multiple times, the query efficiency is not high, try to use join queries instead of subqueries