A brief discussion on several situations where MySQL returns Boolean types

select id='22aa' from mytest where age=202 returns 1 which can be encapsulated as true
select count(*)=1 from mytest where age=202 returns 1 which can be encapsulated as true
select count(*)=0 from mytest where age=202 returns 0 and can be encapsulated as false
select count(*)<3 from mytest where age=202 returns 1 which can be encapsulated as true
select count(*)<=1 from mytest where age=202 returns 1 which can be encapsulated as true
select name="aa" from mytest where age=10 When name is null, sql will not report an error, and the returned result is also null. Refer to the sql 3 code in the second case and an error will be reported.

select enable from mytest where age=202 returns 1 which can be packaged as true
select count(*) from mytest returns 4 which can be encapsulated as Boolean type, but is false
select enable from mytest where age=201 returns null. Cannot be encapsulated as Boolean type. The code will report an error directly. select id from mytest where age=202 returns '22aa'. Can be encapsulated as Boolean type, but it is false.
select id from mytest where age=202 returns 'true' Can be encapsulated as Boolean type, but is true
select id from mytest where age=202 returns 'false' which can be encapsulated as Boolean type, false
//Special case select * from mytest Error Expected one result (or null) to be returned by selectOne(), but found: 4
select * from mytest where age=202 returns a set of data false 2019-08-28 202 15 1 , which can be encapsulated as false
select * from mytest where age=202 returns a set of data true 2019-08-28 202 15 1 , which can be encapsulated as true
select * from mytest where age=202 returns a set of data aaaa2019-08-28 202 15 1 , which can be encapsulated as false

> SELECT COUNT(*) FROM message WHERE message.is_national = 1 AND message.updated_at > '2020-01-01 00:00:00' AND message.deleted_at IS NULL;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
1 row in set
Time: 0.018s
> SELECT COUNT(*) FROM message WHERE message.is_national is true AND message.updated_at > '2020-01-01 00:00:00' AND message.deleted_at IS NULL;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
1 row in set
Time: 2.162s

> EXPLAIN SELECT COUNT(*) FROM message WHERE message.is_national = 1 AND message.updated_at > '2020-01-01 00:00:00' AND message.de
        leted_at IS NULL;
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
| 1 | SIMPLE | message | ref | ix_message_updated_at,idx_updated_at_is_national,ix_message_is_national | ix_message_is_national | 1 | const | 1 | Using where |

> EXPLAIN SELECT COUNT(*) FROM message WHERE message.is_national is true AND message.updated_at > '2020-01-01 00:00:00' AND messageag
        e.deleted_at IS NULL;
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
| 1 | SIMPLE | message | ALL | ix_message_updated_at,idx_updated_at_is_national | <null> | <null> | <null> | a very large number | Using what
re |