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Databases & SQL vocabulary · SQL Statements and Queries

Left join

Meaning in databases & SQL, with examples

nounCore term

In databases & SQL, left join means: A join that returns all rows from the first (left) table and the matching rows from the second; where there is no match, the second table's columns are NULL.

In Turkish: sol birleştirme, left join, sol dış birleştirme

How it is used

Also written LEFT OUTER JOIN; the two mean the same. It is used to keep rows that have no partner, for example customers with no orders. A classic trick is LEFT JOIN ... WHERE right_table.id IS NULL to find rows with no match.

Example sentences

  1. Use a left join so customers without any orders still appear in the list.

  2. Putting a condition on the right table in the WHERE clause turns your left join into an inner join.

Common collocations

  • left join on
  • LEFT OUTER JOIN
  • left join with IS NULL
  • use a left join
  • joinA SQL operation that combines rows from two or more tables using a related column, such as a customer ID. As a verb, to join tables means to combine them this way.
  • inner joinA join that returns only the rows that have a match in both tables; rows without a partner on the other side are left out.
  • NULLA special marker meaning that a value is missing or unknown. It is not the same as zero or an empty string.
  • WHERE clauseThe part of a SQL statement that sets a condition, so only the rows that meet it are read, updated or deleted.

This word in other fields

The same English word can have a different meaning in another field:

More terms: SQL Statements and Queries

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