Find the non null columns in SQL Server in a table

问题

I have read many answers but they are all for PL/SQL or Oracle, I could not find anything for Microsoft SQL-Server.

My table :

CREATE TABLE StudentScore
(
  Student_ID INT PRIMARY KEY,
  Student_Name NVARCHAR (50),
  Student_Score INT
) 

GO

INSERT INTO StudentScore VALUES (1,'Ali', NULL)
INSERT INTO StudentScore VALUES (2,'Zaid', 770)
INSERT INTO StudentScore VALUES (3,'Mohd', 1140)
INSERT INTO StudentScore VALUES (4,NULL, 770)
INSERT INTO StudentScore VALUES (5,'John', 1240)
INSERT INTO StudentScore VALUES (6,'Mike', 1140)
INSERT INTO StudentScore VALUES (7,'Goerge', NULL)

How to find the names of all the non-null columns.
Return table containing only non null columns

EDIT based on comments:

I am aware of IS_NULLABLE attribute of Information_schema . But just because a column allows null values does not mean it will actually have null values. How to find out columns which actually have null values.

I am looking for some num_nulls equivalent for microsoft SQL-SERVER.

回答1:

You could achieve it by issuing:

SELECT 
  FORMATMESSAGE('SELECT col = ''%s.%s.%s'' FROM %s.%s HAVING COUNT(*) != COUNT(%s)', 
     QUOTENAME(TABLE_SCHEMA),
     QUOTENAME(TABLE_NAME),
     QUOTENAME(COLUMN_NAME),
     QUOTENAME(TABLE_SCHEMA),
     QUOTENAME(TABLE_NAME),
     QUOTENAME(COLUMN_NAME)
  )
FROM INFORMATION_SCHEMA.COLUMNS
WHERE IS_NULLABLE = 'YES';

db<>fiddle demo

It will generate script for checking individual column.

HAVING COUNT(*) != COUNT(col_name) -- it means that column contains at least single NULL

HAVING COUNT(col_name) = 0 AND COUNT(*) != 0 -- it means all values in columns are NULL

This approach could be polished with using STRING_AGG to get single query per table and with dynamic SQL you could avoid the need of copying the query.

EDIT:

Fully baked-solution:

DECLARE @sql NVARCHAR(MAX);

SELECT @sql = STRING_AGG(
  FORMATMESSAGE('SELECT table_schema = ''%s''
                        ,table_name = ''%s''
                        ,table_col_name = ''%s'' 
                        ,row_num = COUNT(*)
                        ,row_num_non_nulls = COUNT(%s)
                        ,row_num_nulls = COUNT(*) - COUNT(%s)
                 FROM %s.%s', 
     QUOTENAME(TABLE_SCHEMA),
     QUOTENAME(TABLE_NAME),
     QUOTENAME(COLUMN_NAME),
     QUOTENAME(COLUMN_NAME),
     QUOTENAME(COLUMN_NAME),
     QUOTENAME(TABLE_SCHEMA),
     QUOTENAME(TABLE_NAME),
     QUOTENAME(COLUMN_NAME)), ' UNION ALL' + CHAR(13)
               ) WITHIN GROUP(ORDER BY TABLE_SCHEMA, TABLE_NAME)

FROM INFORMATION_SCHEMA.COLUMNS
WHERE IS_NULLABLE = 'YES'
  AND TABLE_NAME = ?        -- filter by table name
  AND TABLE_SCHEMA = ?;     -- filter by schema name

SELECT @sql;
EXEC(@sql);

db<>fiddle demo

Output:

+---------------+-----------------+------------------+----------+--------------------+---------------+
| table_schema  |   table_name    | table_col_name   | row_num  | row_num_non_nulls  | row_num_nulls |
+---------------+-----------------+------------------+----------+--------------------+---------------+
| [dbo]         | [StudentScore]  | [Student_Name]   |       7  |                 6  |             1 |
| [dbo]         | [StudentScore]  | [Student_Score]  |       7  |                 5  |             2 |
+---------------+-----------------+------------------+----------+--------------------+---------------+

回答2:

Perhaps you want to look at INFORMATION_SCHEMA.COLUMNS. The column IS_NULLABLE provides this information.

Note that the INFORMATION_SCHEMA tables (well, they are really views) are Standard SQL, so this information is available in most database. Oracle has not (yet?) adopted them.

来源：https://stackoverflow.com/questions/61426544/find-the-non-null-columns-in-sql-server-in-a-table

标签

sql

sql-server

tsql