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create table grass_test1 (i1 integer, d1 double precision, c1 varchar(20))

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insert into grass_test1 values ( 1, 123.456, 'abcd' )

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insert into grass_test1 values ( 2, null, 'xxx' )

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select * from grass_test1
1|123.456|abcd
2||xxx

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select c1 from grass_test1 where d1 < 500 / 2 and i1 <> 2  and c1 ~ 'bc' 
abcd

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insert into grass_test1 values ( 3, 0.0, '_\''_' )

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alter table grass_test1 add column i2 integer

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update grass_test1 set d1 = 18.6, i2 = 987  where i1 = 2

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select * from grass_test1
1|123.456|abcd|
2|18.6|xxx|987
3|0|_\'_|

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drop table grass_test1