MySQL細節

Alter table

ALTER TABLE <table> DROP <column>;
ALTER TABLE <table> ADD <column> <data_type>;
ALTER TABLE <table> ADD <column> <data_type> [ FIRST | [AFTER <column>] ];
ALTER TABLE <table> MODIFY <column> <data type>;
ALTER TABLE <table> CHANGE <old_column_name> <new_column_name> <data_type>;

Vertical seperation and horizonal seperation of table query

# Vertical division.
SELECT <col_1>, <col_2> FROM <table>;
SELECT <col_3>, <col_4> FROM <table>;

# Horizontal division.
SELECT <col_1>, <col_2> FROM <table> LIMIT <max_row> OFFSET <start_row>;
SELECT <col_1>, <col_2> FROM <table> LIMIT <max_row> OFFSET <start_row>;

Examine the global varriable

# Examine all global variables.
SHOW VARIABLES;

# Examine all all global variables about the code-encoding.
SHOW VARIABLES LIKE 'character_set_%';
# Some important global variables about the code-encoding:
# character_set_client
# character_set_connection
# character_set_database
# character_set_results
# character_set_server
# character_set_system
# character_sets_dir