Data Cleanup Strategies Before Importing to SQL from Excel

Check for Required Fields

If a database column doesn't allow NULL, every row needs a value.

Use conditional formatting to highlight blanks:
Home → Conditional Formatting → New Rule → “Format only cells that contain” → Blanks

Or use COUNTBLANK() to count how many empties exist.

Validate Data Types

Common mismatches:

• Numbers as text: Check alignment (left = text, right = number)
• Dates as text: ISNUMBER() returns FALSE for text dates
• Leading zeros stripped: Format as text or use apostrophe prefix

Convert text to numbers: Data → Text to Columns (just click Finish to trigger conversion).

Trim Whitespace

Leading and trailing spaces cause matching failures and look identical to clean data.

=TRIM(A1) removes extra spaces.

For hidden characters (line breaks, non-breaking spaces): =CLEAN(TRIM(A1))

Check for Duplicates

If the database has a unique constraint, duplicate values will cause import failure.

Conditional Formatting → Highlight Cells Rules → Duplicate Values

Or use COUNTIF to find duplicates: =COUNTIF(A:A, A1)>1

Validate Foreign Keys

If your data references another table (like CustomerID pointing to a Customers table), verify all values exist.

Import the valid values list from the database, then use VLOOKUP or MATCH to check:
=IFERROR(MATCH(A1, ValidCustomers, 0), "INVALID")

Official Resources

• Clean data import — data cleaning techniques
• Import from Excel to SQL — SQL Server import guide