Generated Key Column In Table Comparison
- Specify the column of the comparison table with unique keys i.e. By design contains no duplicate keys as the Generated key column. A generated key column indicates which row of a set containing identical primary keys is to be used in the comparison. This provides a method of handling duplicate keys in the comparison table.
- Apr 23, 2019 This video explains about GENERATED KEY COLUMN feature of table comparison. Visit the below tutorials before viewing this: Basics of Table Comparison: https.
- A generated column definition can refer to other generated columns, but only those occurring earlier in the table definition. A generated column definition can refer to any base (nongenerated) column in the table whether its definition occurs earlier or later.
Say you have requirement to compare two tables. You have two tables in same database or server that you wish to compare, and check if any changes in the column values or see if any row is missing in either of tables.
Below are some of the methods you can use to compare two tables in SQL.
The comparison table (that are not of the long or blob data type or the Generated key column) are used as compare columns. You do not need to add primary key columns to the compare column list. They are always compared before the compare columns apply. The compare columns apply only if.
Compare Two Tables using UNION ALL
UNION allows you to compare data from two similar tables or data sets. It also handles the NULL values to other NULL values which JOIN or WHERE clause doesn’t handle. It allows quickly checking what are the data missing or changed in either table.
The above query returns the all rows from both tables as old and new. You can quickly verify the differences between two tables.
Related reading: Steps to Optimize SQL Query Performance
Compare Two Table using MINUS
You can compare the two similar tables or data sets using MINUS operator. It returns all rows in table 1 that do not exist or changed in the other table.
You can quickly check how many records are having mismatch between two tables.
Monster hunter generations ultimate low rank key quests 2017. The only drawback with using UNION and MINUS is that the tables must have the same number of columns and the data types must match.
Compare Two Table using JOIN
This is the easiest but user has to do some additional work to get the correct result. In this approach you can join the two tables on the primary key of the two tables and use case statement to check whether particular column is matching between two tables.
The only drawback of using JOIN is, it cannot compare the NULL values, and you should use the NVL on the column that may have null values in it.
Compare Two Table using NOT EXISTS
Generated Column Mysql
The other faster method is to use the NOT EXISTS in WHERE clause of the query. This method is faster and performs well on the large volume of data.
In this approach also you have to use the NVL on the columns which contains NULL in it.
Generated Key Column In Table Comparison Examples
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