alter-table

问题 Can the datatype of a field be changed to int from nvarchar?? alter table employee alter column designation int is this valid?? If not can it be done in some other way?? P.S: I am using MS SQL Server 回答1: You can try doing an alter table. If it fails do this: Create a new column that's an integer: ALTER TABLE tableName ADD newCol int; Select the data from the old column into the new one: UPDATE tableName SET newCol = CAST(oldCol AS int) ; Drop the old column 回答2: It is possible only when you

问题 Can the datatype of a field be changed to int from nvarchar?? alter table employee alter column designation int is this valid?? If not can it be done in some other way?? P.S: I am using MS SQL Server 回答1: You can try doing an alter table. If it fails do this: Create a new column that's an integer: ALTER TABLE tableName ADD newCol int; Select the data from the old column into the new one: UPDATE tableName SET newCol = CAST(oldCol AS int) ; Drop the old column 回答2: It is possible only when you

问题 I have a very large table that I want to add a timestamp column to. It is a table that gets a lot more updates than inserts. I am trying to figure out a way to do this without taking the table out of production for a significant amount of time and it has me in knots. I can do: alter table stuff add column mod_time timestamp; Well, I could do this and then the table is locked for 3-5 hours. Not a happy time for users. For adding a varchar column, for example, I could create a new table, add

问题 I use MS Access (2003) database. Once I create a column I set NOT NULL using sql statement: ALTER TABLE Table1 ALTER column myColumn INTEGER not null Is there a way to change it back to allow null values? I already tried: ALTER TABLE Table1 ALTER column myColumn INTEGER null but nothing... 回答1: You cant specify null in ALTER TABLE (although not null is allowed) See the below documentation and also this discussion on this toppic Syntax ALTER TABLE table {ADD {COLUMN field type[(size)] [NOT

问题 My date format of "03-01-2017 10:24:48" is getting stored in SQL as "2017-03-01 10:24:48.000" where my 'dd-mm-yyyy' format is getting converted to 'yyyy-mm-dd' format. How can I change the date format of the column to my desired format? My table already contains data. 回答1: SQL Server doesn't store a DateTime in any string format - it's stored as an 8 byte numerical (binary) value. The various settings (language, date format) only influence how the DateTime is shown to you in SQL Server

问题 I got an issue When some table on the development database has more columns added, and right now I should add the column in the production database. I try to add the column manually, by Add Column on Table Tree, but when I try to save, it show me a warning : here's the complete warning message : Saving Definition Changes to tables with large amounts of data could take a considerable amount of time. While changes are being saved, table data will not be accessible. is this safe? or is there

问题 I'm trying to add a new column ALTER TABLE "Cidade" ADD COLUMN "BoundBox" VARCHAR(255) to this table: "Cidade" "Id" integer not null constraint "Cidade_PK" primary key, "Nome" varchar(120), "EstadoId" integer not null constraint "Estado_Cidade_FK" references "Estado", "PontoCentralLatitude" numeric, "PontoCentralLongitude" numeric But the query never finish, I've already waited for 5 minutes and nothing happened. The table has only 5,000 records, and I can't wait too much time since it block

问题 I'm trying to add a column to a table in my Postgres 9.3 database with this seemingly simple SQL: ALTER TABLE quizzes ADD COLUMN deleted BOOLEAN NOT NULL DEFAULT false; However, I'm getting the following error: ERROR: could not create unique index "quizzes_pkey" DETAIL: Key (id)=(10557462) is duplicated. Strangely enough, there are actually no rows with that id (which is the primary key, so it shouldn't have duplicates): SELECT id FROM quizzes WHERE id = 10557462; id ---- (0 rows) In fact, it

问题 I'm trying to add a column to a table in my Postgres 9.3 database with this seemingly simple SQL: ALTER TABLE quizzes ADD COLUMN deleted BOOLEAN NOT NULL DEFAULT false; However, I'm getting the following error: ERROR: could not create unique index "quizzes_pkey" DETAIL: Key (id)=(10557462) is duplicated. Strangely enough, there are actually no rows with that id (which is the primary key, so it shouldn't have duplicates): SELECT id FROM quizzes WHERE id = 10557462; id ---- (0 rows) In fact, it

问题 Is it possible to rename a column in MySQL without having to repeat its type definition? Please without having to hack into information_schema. 回答1: The ALTER TABLE syntax does not seem to offer such possibility: ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name [alter_specification [, alter_specification] ...] [partition_options] ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name partition_options alter_specification: table_options [...] | CHANGE [COLUMN] old_col_name new_col_name column