SN9zCvSA

1How to check if referenced table is not empty?
2CREATE TABLE IF NOT EXISTS master(
3    master_id      INT          NOT NULL AUTO_INCREMENT,
4    master_name    VARCHAR(15) NOT NULL,
5    PRIMARY KEY(master_id)
6) TYPE=InnoDB CHARACTER SET=UTF8;
7	
8CREATE TABLE IF NOT EXISTS slave(
9    slave_id        INT          NOT NULL AUTO_INCREMENT,
10    slave_name      VARCHAR(15)  NOT NULL,
11    master_id       INT
12    PRIMARY KEY (slave_id), 
13    FOREIGN KEY (master_id) REFERENCES master(master_id)
14) TYPE=InnoDB CHARACTER SET=UTF8;
15	
16SELECT COUNT(*) as number_of_connections
17  FROM master m
18  INNER JOIN slave s ON (s.master_id = m.master_id)
19UNION ALL
20  SELECT COUNT(*) as rows_in_slave
21  FROM slave s2
22UNION ALL
23  SELECT COUNT(*) as rows_in_master
24  FROM master m2
25	
26SELECT COUNT(*) FROM slave