ASSUMED UNIQUE (column constraint) ASSUMED UNIQUE ( column_name ) (table constraint) The UNIQUE constraint specifies that a group of one or moreĬolumns of a table can contain only unique values. If there is no default forĪ column, then the default is null. The default expression will be used in any insert operation thatĭoes not specify a value for the column. The data type of theĭefault expression must match the data type of the column. Variable-free expression (subqueries and cross-references to otherĬolumns in the current table are not allowed). Whose column definition it appears within. DEFAULT The DEFAULT clause assigns a default data value for the column Its use is discouraged in new applications. This clause is only provided for compatibility with non-standard SQLĭatabases. NULL The column is allowed to contain null values. NOT NULL The column is not allowed to contain null values. COLLATE collation The COLLATE clause assigns a collation to the column (which mustīe of a collatable data type). The name of a column to be created in the new table. The name (optionally schema-qualified) of the table to be created. Like the one that would have been created. Note that there is no guarantee that the existing table is anything IF NOT EXISTS Do not throw an error if a table with the same name already exists. Any indexes created on a temporary table are automatically Table exists, unless they are referenced with schema-qualified Same name are not visible to the current session while the temporary Tables are automatically dropped at the end of a session and are Parameters TEMPORARY or TEMP If specified, the table is created as a temporary table. Every columnĬonstraint can also be written as a table constraint a columnĬonstraint is only a notational convenience for use when the constraint ![]() A table constraint definition is not tied to a particularĬolumn, and it can encompass more than one column. A column constraint is defined as part of a columnĭefinition. There are two ways to define constraints: table constraints and columnĬonstraints. Guaranteed on the database side if the application violates its assumed ![]() When the constraint in question is enforced. Instead, Hyper assumes that the constraints are enforced by the client,Īnd thus it performs all useful optimizations that are only possible The constraints are not actually verified when rows are modified. Hyper only officially supports ASSUMED constraints, which means that Updated rows must satisfy for an insert or update operation to succeed.Ī constraint is an SQL object that helps define the set of valid values The optional constraint clauses specify constraints (tests) that new or The name of the table must beĭistinct from the name of any other table, sequence, index, view, or Temporary tables exist in a special schema, so a schema name cannot be Otherwise it is created in the current schema. The table will be owned by the user issuing the command.ĬREATE TABLE myschema.mytable. When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values.CREATE TABLE will create a new, initially empty table in the currentĭatabase. 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. sequence_option is an option supported by ALTER SEQUENCE such as INCREMENT BY. These forms alter the sequence that underlies an existing identity column. If DROP IDENTITY IF EXISTS is specified and the column is not an identity column, no error is thrown. Like SET DEFAULT, these forms only affect the behavior of subsequent INSERT and UPDATE commands they do not cause rows already in the table to change. These forms change whether a column is an identity column or change the generation attribute of an existing identity column. RENAME CONSTRAINT constraint_name TO new_constraint_nameĪLTER TABLE ALL IN TABLESPACE name ]ĪTTACH PARTITION partition_name AS IDENTITY
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