MERGE INTO table_name table1
USING table_name2 table2
ON (table1.col1=table2.col2)
WHEN MATCHED THEN
UPDATE SET
table1.col1=table2.col2,
table1.col2=table2.col3,
...
WHEN NOT MATCHED THEN
INSERT VALUES(table2.col1,table2.col2,table2.col3,...); -----合并语句
##################### CREATE/ALTER TABLE #######################
alter table table_name drop column column_name ;---drop column
alter table table_name set unused (col1,col2,...);----设置列无效，这个比较快。
alter table table_name drop unused columns;---删除被设为无效的列
rename table_name1 to table_name2; ---重命名表
comment on table table_name is ’comment message’;----给表放入注释信息
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