![]() When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values. n_distinct affects the statistics for the table itself, while n_distinct_inherited affects the statistics gathered for the table plus its inheritance children. Currently, the only defined per-attribute options are n_distinct and n_distinct_inherited, which override the number-of-distinct-values estimates made by subsequent ANALYZE operations. This form sets or resets per-attribute options. SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. For more information on the use of statistics by the PostgreSQL query planner, refer to Section 14.2. The target can be set in the range 0 to 10000 alternatively, set it to -1 to revert to using the system default statistics target ( default_statistics_target). This form sets the per-column statistics-gathering target for subsequent ANALYZE operations. You can only use SET NOT NULL when the column contains no null values. These forms change whether a column is marked to allow null values or to reject null values. Default values only apply in subsequent INSERT or UPDATE commands they do not cause rows already in the table to change. These forms set or remove the default value for a column. A USING clause must be provided if there is no implicit or assignment cast from old to new type. The optional USING clause specifies how to compute the new column value from the old if omitted, the default conversion is the same as an assignment cast from old data type to new. The optional COLLATE clause specifies a collation for the new column if omitted, the collation is the default for the new column type. ![]() Indexes and simple table constraints involving the column will be automatically converted to use the new column type by reparsing the originally supplied expression. This form changes the type of a column of a table. IF EXISTSĭo not throw an error if the table does not exist. If IF EXISTS is specified and the column does not exist, no error is thrown. You will need to say CASCADE if anything outside the table depends on the column, for example, foreign key references or views. Indexes and table constraints involving the column will be automatically dropped as well. This form adds a new column to the table, using the same syntax as CREATE TABLE. RENAME CONSTRAINT constraint_name TO new_constraint_nameĪLTER TABLE ALL IN TABLESPACE name ]ĪDD column_name data_type ]ĭROP column_name ĪLTER column_name TYPE data_type ĪLTER column_name SET DEFAULT expressionĪLTER column_name DROP DEFAULTĪLTER column_name USING INDEX index_name That would be incorrect – you’d be better off with the next solution.Īnother workaround is to use filtered indexes.Synopsis ALTER TABLE name ĪLTER TABLE name You’re going to think that someday, if the majority of your records are deleted, then you might even want IsDeleted to be the leading key in all of your indexes. Over time, it starts to become more important. In the beginning, it doesn’t matter if IsDeleted is part of the key or the includes – because it’s not filtering anything out yet. One workaround is to add IsDeleted to every index. When you first implement soft deletes, this isn’t a huge concern for most queries because none of your data can be excluded (because no rows have IsDeleted = 1 yet.) However, the worst case for performance is a query that used to have a covering index, but now has to do a key lookup for every single row in order to double-check that the row hasn’t been deleted yet. That also means that your missing index recommendations are going to ask for IsDeleted in the key of your index: Whether use the view approach or add IsDeleted = 0 to all your queries, your execution plans are going to have something new: a filter on IsDeleted = 0. I’m just using the * here for simplicity.)ĭoing the table-to-view switcheroo means the soft-deleted rows are instantly filtered out from my queries. Under the covers, SQL Server builds the code for the view once, and then if you add more columns to dbo.Users_tbl, the new columns won’t show up in queries until you call sp_refreshview. (Quick note: you probably don’t want to use SELECT * in a view like this.
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