SQL: inner join, left join, right join, full join usage and meaning

The join syntax is as follows: select [field] from [Table Name 1] inner/left/right/full join [Table name 2] on [Table Name 1. field 1] <relational operator> [Table name 2. field 2] cross join: the product of the flute. without any constraints, the number of rows in a table is multiplied by the number of rows in another table. Left join: return all rows of table name 1. Replace null values with records that do not meet the on condition in table name 2. Ristmjoin: returns all rows with table name 2. Replace null values with records that do not meet the on condition in table name 1. Full join: return all records in the two tables. Replace null values with records that do not meet the on condition. Inner JON: returns only records that meet the on condition in both tables.