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SELECT emp_no FROM employees.salaries union select emp_no from employees.salaries;
EXPLAIN SELECT emp_no FROM employees.salaries union select emp_no from employees.salaries;
EXPLAIN SELECT emp_no FROM employees.salaries union all select emp_no from employees.salaries;
select count(*) from employees.salaries;
explain select * from (select * from employees.salaries) as Pp;
select cc.first_name, cc.salary from (select salaries.emp_no, salaries.salary, employees.first_name from employees.salaries join employees.employees on salaries.emp_no=employees.emp_no where salary > (select avg(salaries.salary) from employees.salaries)) as cc;
select avg(salaries.salary) from employees.salaries;
desc select salaries.emp_no, salaries.salary, employees.first_name from employees.salaries join employees.employees on salaries.emp_no=employees.emp_no;
explain select count(distinct salary) from employees.salaries;
show indexes from employees.salaries; alter table employees.salaries add index keke(salary); explain select distinct salary from employees.salaries order by salary ;
show variables like 'slow%';
set global slow_query_log='ON'; set global slow_launch_time=1; use employees; CREATE TABLE employees.t1 (s1 INT, s2 CHAR(5), s3 FLOAT);
INSERT INTO employees.t1 VALUES (1,'1',1.0); INSERT INTO employees.t1 VALUES (2,'2',2.0); explain SELECT sb1,sb2,sb3 FROM (SELECT s1 AS sb1, s2 AS sb2, s3*2 AS sb3 FROM employees.t1) AS sb WHERE sb1 > 1;
SELECT AVG(SUM(column1)) FROM t1 GROUP BY column1;
explain SELECT AVG(sum_column1) FROM (SELECT SUM(s1) AS sum_column1 FROM t1 GROUP BY s1) AS t1;
explain SELECT AVG(sum_column1) FROM (SELECT SUM(s1) AS sum_column1 FROM t1) AS t1;
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