# Establish connection con1 (user=root)
# Establish connection con2 (user=root)
# Establish connection con3 (user=root)
# Drop test table
drop table if exists t;
# Create test table
create table t(a INT PRIMARY KEY, b INT) engine=InnoDB;
# Insert two rows to test table
insert into t values(2,1);
insert into t values(1,2);
# Switch to connection con1
BEGIN;
SELECT b FROM t WHERE a=1 FOR UPDATE;
b
2
# Switch to connection con2
BEGIN;
SELECT b FROM t WHERE a=2 FOR UPDATE;
b
1
# Switch to connection con1
SELECT b FROM t WHERE a=2 FOR UPDATE;
# Switch to connection con2
SELECT b FROM t WHERE a=1 FOR UPDATE;
# Switch to connection con3
1
# Drop test table
drop table t;