How to Compare Table and View Structures to Avoid Insert Errors in SQL

 

When working with databases, especially in complex systems, you’ll often need to insert data from one object, such as a view, into another, like a table. However, if the structures of these two objects are not perfectly aligned—due to differences in data types, column lengths, or precision—you might run into various issues such as data truncation, conversion errors, or even complete failures of your SQL queries.

In this blog post, I’ll show you a handy SQL query that compares the column definitions between a table and a view, highlighting any mismatches that could potentially cause insert errors.

Why Do We Need to Compare Table and View Structures?

Imagine you have a view that gathers data from multiple tables, and you want to insert the data from this view into a table. If the columns in the view have different data types or lengths compared to the table, you can face problems like:

• Data truncation: When the view has longer string fields than the table, any data that exceeds the table's limits will be truncated.
• Type conversion errors: If a column in the view is of a different type than its counterpart in the table (e.g., VARCHAR vs. INT), SQL will throw an error when you try to insert.
• Precision loss: When dealing with numeric data, mismatches in precision or scale between the view and the table can cause rounding errors or fail entirely.

By using a comparison query, you can spot these differences before running your insert statement, allowing you to make any necessary adjustments in advance.

The SQL Query to Compare Table and View Structures

The following SQL query compares the structure of a table and a view by looking at their column definitions. It checks for differences in data types, character lengths, and numeric precision/scale.

SELECT 

    t.COLUMN_NAME,

    t.DATA_TYPE AS Table_Data_Type,

    t.CHARACTER_MAXIMUM_LENGTH AS Table_Max_Length,

    t.NUMERIC_PRECISION AS Table_Precision,

    t.NUMERIC_SCALE AS Table_Scale,

    v.DATA_TYPE AS View_Data_Type,

    v.CHARACTER_MAXIMUM_LENGTH AS View_Max_Length,

    v.NUMERIC_PRECISION AS View_Precision,

    v.NUMERIC_SCALE AS View_Scale

FROM 

    INFORMATION_SCHEMA.COLUMNS t

INNER JOIN 

    INFORMATION_SCHEMA.COLUMNS v

    ON t.COLUMN_NAME = v.COLUMN_NAME

WHERE 

    t.TABLE_NAME = 'table1' AND 

    v.TABLE_NAME = 'TableView2' AND

    (

        t.DATA_TYPE <> v.DATA_TYPE OR

        (t.CHARACTER_MAXIMUM_LENGTH <> v.CHARACTER_MAXIMUM_LENGTH) OR

        (t.NUMERIC_PRECISION <> v.NUMERIC_PRECISION) OR

        (t.NUMERIC_SCALE <> v.NUMERIC_SCALE)

    )

ORDER BY 

    t.COLUMN_NAME;