VLOOKUP PostgreSQL Solution
Tags: tutorial, beginners, database, datascience
Published: 2023-01-11 12:35:49

When working with large datasets in PostgreSQL, the "WHERE IN" clause is a powerful tool for filtering results based on a list of specific values. However, one limitation of this clause is that it returns the results in a different order than the inputted data. This can be a problem if the order of the results is important for further analysis or manipulation.

> Case :

Once I have a task, but I found that I possess an incomplete table, as seen below:

Table 1 - Raw Data

| User ID | User Code | Third-Party User ID |
|---------|-----------|---------------------|
| 123     |           |                     |
| 456     |           |                     |
| 789     |           |                     |
| 101     |           |                     |

To rectify this, I attempted to utilize the PostgreSQL `WHERE IN` clause along with a list of User IDs to complete the table. However, I encountered an issue in which the results returned were not in the same order as the inputted data. This resulted in my inability to copy the data over as desired.

> Solution :

To solve this problem, we can use a VLOOKUP function in a spreadsheet program such as Excel or Google Sheets. A VLOOKUP function allows you to search for a specific value in a table and return a corresponding value from another column in the same row.

First, we would need to create a separate spreadsheet that contains the User ID, User Code, and Third-Party User ID of all users. We'll call this spreadsheet "User Data" and it should be set up as follows:

Table 2 - Query result

| User ID | User Code | Third-Party User ID |
|---------|-----------|---------------------|
| 789     | ABC123    | XYZ456              |
| 101     | DEF456    | ZYX789              |
| 456     | GHI789    | WVU123              |
| 123     | JKL101    | UTS456              |

Next, we would take our original incomplete table and add a new column for User Code and Third-Party User ID. Then, we would use the VLOOKUP function to match each User ID in the original table with the corresponding User Code and Third-Party User ID from the "User Data" spreadsheet.

The syntax for the VLOOKUP function in Excel would look like this:

```excel
=VLOOKUP(A2, User_Data, 2, FALSE)
```

Where "A2" is the cell containing the User ID for the first row, "User_Data" is the range of cells for the separate table, "2" is the column number for the User Code in that table, and "FALSE" means an exact match is required.

We would then copy and paste the formula down the column for all rows of User ID. We would repeat the step for the Third-Party User ID.

After applying the VLOOKUP function to all User ID in the original table, we can now copy and paste all the data from the original table to the desired location. It will have the same order as the inputted User IDs.

In summary, using a VLOOKUP function in a spreadsheet can solve the limitation of the PostgreSQL "WHERE IN" clause by allowing the steps above to maintain the order of the inputted data while still retrieving the corresponding data from another table. This is a useful technique when working with large datasets and the order of the results is important.