What is the method for conducting a multi-table query in SQLite?

2 years ago
William Carter
2 minutes

There are various methods to perform multi-table queries in SQLite, here are some commonly used options:

  1. Using JOIN clause: the JOIN clause is used to connect multiple tables together and query them based on specified conditions. Commonly used JOIN clauses include INNER JOIN, LEFT JOIN, RIGHT JOIN, etc. For example:
SELECT *
FROM table1
INNER JOIN table2 ON table1.id = table2.id;
  1. By using a subquery: you can nest a subquery within a query statement to combine the results of querying multiple tables. For example:
SELECT *
FROM table1
WHERE table1.id IN (SELECT id FROM table2);
  1. Using the UNION operator: the UNION operator can be used to combine the results of multiple queries into one result set. It’s important to note that when using the UNION operator, the number and types of columns in the queries must match. For example:
SELECT column1 FROM table1
UNION
SELECT column1 FROM table2;
  1. Using the EXISTS keyword: The EXISTS keyword can be used to determine if a certain condition exists in another table. For example:
SELECT *
FROM table1
WHERE EXISTS (SELECT id FROM table2 WHERE table2.id = table1.id);

These methods can be chosen according to specific needs, and different methods may have varying performance based on the size of the data and how indexes are used.

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