Question

到目前为止我发现的其他所有内容都指向sys.columns并返回有关该列的一些元数据。但是，我希望此信息的格式可以在动态SQL中用于在另一个表中创建相同的列。

我遇到的主要问题是对于不允许列宽的int或bit等类型，sys.columns仍然显示长度，精度或比例（在datetime的情况下全部为3））。

有没有办法从列元数据中获取可用的类型？例如，根据列名称，我希望结果返回int或decimal(5,2)等。

Answer 1

在路易斯戴维森偷窃：Utility Queries–Column Metadata - Louis Davidson

SELECT  * 
FROM    ( SELECT    REPLACE(LOWER(objects.type_desc), '_', ' ') AS table_type, schemas.name AS schema_name, objects.name AS table_name, 
                    columns.name AS column_name, CASE WHEN columns.is_identity = 1 THEN 'IDENTITY NOT NULL' 
                                                      WHEN columns.is_nullable = 1 THEN 'NULL' 
                                                      ELSE 'NOT NULL' 
                                                 END AS nullability, 
                   --types that have a ascii character or binary length 
                    CASE WHEN columns.is_computed = 1 THEN 'Computed' 
                         WHEN types.name IN ( 'varchar', 'char', 'varbinary' ) THEN types.name + 
                                         CASE WHEN columns.max_length = -1 THEN '(max)'       
                                                ELSE '(' + CAST(columns.max_length AS VARCHAR(4)) + ')' END       
                         --types that have an unicode character type that requires length to be halved 
                         WHEN types.name IN ( 'nvarchar', 'nchar' ) THEN types.name + 
                                          CASE WHEN columns.max_length = -1 THEN '(max)'       
                                                ELSE '(' + CAST(columns.max_length / 2 AS VARCHAR(4)) + ')'       
                                                                                     END
                          --types with a datetime precision 
                         WHEN types.name IN ( 'time', 'datetime2', 'datetimeoffset' ) THEN types.name + 
                                                                   '(' + CAST(columns.scale AS VARCHAR(4)) + ')' 

                         --types with a precision/scale 
                         WHEN types.name IN ( 'numeric', 'decimal' ) 
                         THEN types.name + '(' + CAST(columns.precision AS VARCHAR(4)) + ',' +
                                                                    CAST(columns.scale AS VARCHAR(4)) + ')'

                        --timestamp should be reported as rowversion 
                         WHEN types.name = 'timestamp' THEN 'rowversion' 
                         --and the rest. Note, float is declared with a bit length, but is 
                         --represented as either float or real in types  
                         ELSE types.name 
                    END AS declared_datatype,

                   --types that have a ascii character or binary length 
                    CASE WHEN baseType.name IN ( 'varchar', 'char', 'varbinary' ) 
                                  THEN baseType.name +
                                              CASE WHEN columns.max_length = -1 THEN '(max)' 
                                                   ELSE '(' + CAST(columns.max_length AS VARCHAR(4)) + ')' 
                                              END 

                         --types that have an unicode character type that requires length to be halved 
                         WHEN baseType.name IN ( 'nvarchar', 'nchar' ) 
                                  THEN baseType.name + 
                                              CASE WHEN columns.max_length = -1 THEN '(max)'       
                                                    ELSE '(' + CAST(columns.max_length / 2 AS VARCHAR(4)) + ')'       
                                              END

                         --types with a datetime precision 
                         WHEN baseType.name IN ( 'time', 'datetime2', 'datetimeoffset' ) 
                                   THEN baseType.name + '(' + CAST(columns.scale AS VARCHAR(4)) + ')'

                         --types with a precision/scale 
                         WHEN baseType.name IN ( 'numeric', 'decimal' ) 
                         THEN baseType.name + '(' + CAST(columns.precision AS VARCHAR(4)) + 
                                                 ',' +  CAST(columns.scale AS VARCHAR(4)) + ')'

                         --timestamp should be reported as rowversion 
                         WHEN baseType.name = 'timestamp' THEN 'rowversion' 
                         --and the rest. Note, float is declared with a bit length, but is 
                         --represented as either float or real in types 
                         ELSE baseType.name 
                    END AS base_datatype, 
                    CASE WHEN EXISTS ( SELECT *       
                                       FROM   sys.key_constraints       
                                                 JOIN sys.indexes       
                                                      ON key_constraints.parent_object_id = indexes.object_id       
                                                          AND key_constraints.unique_index_id = indexes.index_id       
                                                 JOIN sys.index_columns       
                                                      ON index_columns.object_id = indexes.object_id       
                                                          AND index_columns.index_id = indexes.index_id       
                                       WHERE  key_constraints.type = 'PK'       
                                         AND columns.column_id = index_columns.column_id       
                                         AND columns.OBJECT_ID = index_columns.OBJECT_ID ) 
                                  THEN 1       
                          ELSE 0 END AS primary_key_column, 
                    columns.column_id, default_constraints.definition AS default_value, 
                    check_constraints.definition AS column_check_constraint, 
                    CASE WHEN EXISTS ( SELECT   * 
                                       FROM     sys.check_constraints AS cc 
                                       WHERE    cc.parent_object_id = columns.OBJECT_ID 
                                                AND cc.definition LIKE '%~[' + columns.name + '~]%' ESCAPE '~' 
                                                AND cc.parent_column_id = 0 ) THEN 1 
                         ELSE 0 
                    END AS table_check_constraint_reference 
          FROM      sys.columns 
                    JOIN sys.types 
                        ON columns.user_type_id = types.user_type_id 
                    JOIN sys.types AS baseType 
                        ON columns.system_type_id = baseType.system_type_id 
                           AND baseType.user_type_id = baseType.system_type_id 
                    JOIN sys.objects 
                            JOIN sys.schemas 
                                   ON schemas.schema_id = objects.schema_id 
                        ON objects.object_id = columns.OBJECT_ID 
                    LEFT OUTER JOIN sys.default_constraints 
                        ON default_constraints.parent_object_id = columns.object_id 
                              AND default_constraints.parent_column_id = columns.column_id 
                    LEFT OUTER JOIN sys.check_constraints 
                        ON check_constraints.parent_object_id = columns.object_id 
                             AND check_constraints.parent_column_id = columns.column_id ) AS rows 
WHERE   table_type = 'user table' 
              AND schema_name LIKE '%' 
              AND table_name LIKE '%' 
              AND column_name LIKE '%' 
              AND nullability LIKE '%' 
              AND base_datatype LIKE '%' 
              AND declared_datatype LIKE '%' 
ORDER BY table_type, schema_name, table_name, column_id

如何在SQL Server中获取列的数据类型？

1 个答案: