varchar

问题 How to select integer values only from a varchar column in PostgreSQL? If the column contains: abc 70 3g 71 1.5 I'd like to select only: 70 71 I'm struggling to find functions like: is_numeric, is_integer, to do something like this: SELECT column FROM table WHERE isinteger(column) Any ideas? Thank you. 回答1: SELECT column FROM table WHERE column ~ '^\d+$' 来源： https://stackoverflow.com/questions/15163793/how-to-select-integer-values-only-from-a-varchar-column-in-postgresql

问题 How to select integer values only from a varchar column in PostgreSQL? If the column contains: abc 70 3g 71 1.5 I'd like to select only: 70 71 I'm struggling to find functions like: is_numeric, is_integer, to do something like this: SELECT column FROM table WHERE isinteger(column) Any ideas? Thank you. 回答1: SELECT column FROM table WHERE column ~ '^\d+$' 来源： https://stackoverflow.com/questions/15163793/how-to-select-integer-values-only-from-a-varchar-column-in-postgresql

问题 Is VARCHAR(100) any better than VARCHAR(500) from a performance point of view? What about disk usage? Talking about PostgreSQL today, not some database some time in history. 回答1: They are identical. From the PostgreSQL documentation: http://www.postgresql.org/docs/8.3/static/datatype-character.html Tip: There are no performance differences between these three types, apart from increased storage size when using the blank-padded type, and a few extra cycles to check the length when storing into

来源： https://stackoverflow.com/questions/6139597/should-varchar-columns-be-put-at-the-end-of-table-definitions-in-mysql

问题 I am trying to populate the data from table1 to table2 , both have the same number of columns. All the columns in table1 are of type varchar . The columns in table2 could be varchar , int or datetime , etc. My question is how to do the conversion during the populating? This is a sample query that I wrote. I miss the part to do the conversion. Also the format of my datetime is mm/dd/yyyy hh:mm:ss . insert into table2 select s.acty_id, s.notes_datetime, s.notes_data from table1 t right join

问题 Is it possible to change a column type in a SQL Server 2008 database from varchar(255) to varchar(MAX) without having to drop the table and recreate? SQL Server Management Studio throws me an error every time I try to do it using that - but to save myself a headache would be nice to know if I can change the type without having to DROP and CREATE. Thanks 回答1: You should be able to do it using TSQL. Something like ALTER TABLE [table] ALTER COLUMN [column] VARCHAR(MAX) 回答2: 'Saving changes is

问题 Is it possible to change a column type in a SQL Server 2008 database from varchar(255) to varchar(MAX) without having to drop the table and recreate? SQL Server Management Studio throws me an error every time I try to do it using that - but to save myself a headache would be nice to know if I can change the type without having to DROP and CREATE. Thanks 回答1: You should be able to do it using TSQL. Something like ALTER TABLE [table] ALTER COLUMN [column] VARCHAR(MAX) 回答2: 'Saving changes is

问题 I'm trying to update the length of a varchar column from 255 characters to 500 without losing the contents. I've dropped and re-created tables before but I've never been exposed to the alter statement which is what I believe I need to use to do this. I found the documentation here: ALTER TABLE (Transfact-SQL) however I can't make heads or tails of it. I have the following so far (essentially nothing unfortunately): alter table [progennet_dev].PROGEN.LE alter column UR_VALUE_3 How do I

问题 I was reading MySQL documentation and I was wondering whether MyISAM's "static" table format also applies on InnoDB or not? Do I gain performance, if I use CHAR instead of VARCHAR when the real lengths varies between 0 and 100 characters or is using VARCHAR(100) better? 回答1: InnoDB does have fixed-width rows and there can be some advantage to declaring all columns in a table as fixed-width. The main benefit is that all "holes" in a page can be reused for any insertion, since all rows are the

问题 I was reading MySQL documentation and I was wondering whether MyISAM's "static" table format also applies on InnoDB or not? Do I gain performance, if I use CHAR instead of VARCHAR when the real lengths varies between 0 and 100 characters or is using VARCHAR(100) better? 回答1: InnoDB does have fixed-width rows and there can be some advantage to declaring all columns in a table as fixed-width. The main benefit is that all "holes" in a page can be reused for any insertion, since all rows are the