![]() ![]() In all other cases, this is a fast operation. That requires a full table scan to verify the column(s) contain no NULL, then this command will attempt to do ALTER COLUMN SET NOT NULL against each such column. Index's columns are not already marked NOT Restrictions ensure that the index is equivalent to one that would The index cannot have expression columns nor be a partial index.Īlso, it must be a b-tree index with default sort ordering. But the database will not assume that theĬonstraint holds for all rows in the table, until it is validatedĮxisting unique index. Keys and they'll fail unless the new row matches the specifiedĬheck constraints). Is a matching row in the referenced table, in the case of foreign Subsequent inserts or updates (that is, they'll fail unless there The constraint will still be enforced against NOT VALID, the potentially-lengthy initialĬheck to verify that all rows in the table satisfy the constraint NOT VALID, which is currently only allowedįor foreign key and CHECK constraints. This form adds a new constraint to a table using the same syntax Strategy to be pursued during future table updates. On very large text and bytea values run faster, at the penalty of increasedĭoesn't itself change anything in the table, it just sets the Of EXTERNAL will make substring operations EXTERNAL is for external, uncompressed data, andĮXTENDED is for external, compressed data. Must be used for fixed-length values such as integer and is inline, uncompressed. Whether this column is held inline or in a secondary This form sets the storage mode for a column. ![]() For more information on the use of statistics by the Value of 0 to revert to estimating the number of distinct values In the table is not performed until query planning time. This can be useful when the size of the tableĬhanges over time, since the multiplication by the number of rows ForĮxample, a value of -1 implies that all values in the column areĭistinct, while a value of -0.5 implies that each value appears Table the exact count is to be computed by multiplying theĮstimated table size by the absolute value of the given number. Negative value, which must be greater than or equal to -1,ĭistinct nonnull values in the column is linear in the size of the The specified number of distinct nonnull values. When set to a positive value, ANALYZE will assume that the column contains exactly The statistics gathered for the table plus its inheritanceĬhildren. Itself, while n_distinct_inherited affects n_distinct affects the statistics for the table ![]() Number-of-distinct-values estimates made by subsequent ANALYZE operations. Only defined per-attribute options are n_distinct and n_distinct_inherited, which override the This form sets or resets per-attribute options. 1 to revert to using the system default statistics targetįor more information on the use of statistics by the PostgreSQL query planner, refer to Section 14.2. Target can be set in the range 0 to 10000 alternatively, set it to This form sets the per-column statistics-gathering target for You can only use SET NOT NULL when the column contains no null These forms change whether a column is marked to allow null They do not cause rows already in the table to change. These forms set or remove the default value for a column.ĭefault values only apply in subsequent INSERT or UPDATE commands No implicit or assignment cast from old to new type. USING clause must be provided if there is Is the same as an assignment cast from old data type to new. New column value from the old if omitted, the default conversion USING clause specifies how to compute the The optional COLLATEĬlause specifies a collation for the new column if omitted, theĬollation is the default for the new column type. Simple table constraints involving the column will be automaticallyĬonverted to use the new column type by reparsing the originally This form changes the type of a column of a table. IF EXISTSĭo not throw an error if the table does not exist. Indexes and tableĬonstraints involving the column will be automatically dropped asĪnything outside the table depends on the column, for example,ĮXISTS is specified and the column does not exist, no error is This form adds a new column to the table, using the same syntaxĪs CREATE TABLE. SET SCHEMA new_schema where action is one of: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 RENAME CONSTRAINT constraint_name TO new_constraint_name Synopsis ALTER TABLE name ĪLTER TABLE name ![]()
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