query multiple tables sql code example

Example 1: join multiple tables sql

SELECT TableA.*, TableB.*, TableC.*, TableD.*
FROM TableA
    JOIN TableB
        ON TableB.aID = TableA.aID
    JOIN TableC
        ON TableC.cID = TableB.cID
    JOIN TableD
        ON TableD.dID = TableA.dID
WHERE DATE(TableC.date)=date(now())

Example 2: sql query multiple tables

-- With JOIN
-- No row if id does not exist in t2
SELECT t1.name, t2.salary FROM t1 JOIN t2 on t1.id = t2.id;
-- A row with a NULL salary is returned if id does not exist in t2
SELECT t1.name, t2.salary FROM t1 LEFT OUTER JOIN t2 on t1.id = t2.id;

-- With UNION: distinct values
SELECT emp_name AS name from employees
UNION
SELECT cust_name AS name from customers;

-- With UNION ALL: keeps duplicates (faster)
SELECT emp_name AS name from employees
UNION ALL
SELECT cust_name AS name from customers;