Convert XLSX to SDF

A Windows application built on SQL Server Compact may require an .sdf database instead of an Excel workbook. Converting the workbook maps its worksheet data into relational tables that the application can query and distribute as a single database file.

What the XLSX format is

.xlsx is the Office Open XML workbook format used by Microsoft Excel, LibreOffice Calc, and other spreadsheet software. It is a ZIP-based package containing worksheets, cells, formulas, formatting, charts, named ranges, and other workbook metadata.

In database workflows, an XLSX file may be a user-maintained spreadsheet, an Excel export, or a data-exchange file containing one or more table-like worksheets. A worksheet is not automatically a relational table: blank rows, merged cells, repeated headers, notes, totals, and mixed data types must be cleaned or mapped before import.

What the SDF format is

In the Databases category, .sdf most commonly denotes a SQL Server Compact database, also called SQL Server CE. It is a single-file relational database containing tables, columns, indexes, constraints, and data. Applications access it through a SQL Server Compact provider, not through Excel.

SQL Server Compact is useful for older Windows desktop, embedded, and mobile software that needs a local database without a separate database server. The file is portable and easy to deploy with an application, but SQL Server Compact is discontinued. New software should generally use a maintained alternative such as SQLite or SQL Server Express unless the receiving application specifically requires an SDF file. The extension is not a universal identifier, so confirm the required SQL Server Compact generation, commonly 3.5 or 4.0, before creating the file.

How to convert XLSX to SDF

A Windows database migration utility that explicitly supports both Excel and SQL Server Compact is the simplest direct option. Full Convert is one commercial example; verify its current SQL Server Compact support and the destination version before purchasing or running a conversion.

1. Make a copy of the workbook. Remove unrelated worksheets, decorative rows, merged layouts, hidden columns, and presentation-only content.
2. Open the migration utility, create a conversion project, select Microsoft Excel as the source, and choose the .xlsx file.
3. Select SQL Server Compact or SQL Server CE as the destination, specify a new filename such as customers.sdf, and select the version required by the consuming application.
4. Map each worksheet that represents a table. Identify the header row, remove duplicate or invalid column names, and exclude columns that should not be stored.
5. Review every destination type. Use text for identifiers with leading zeroes, integer for whole numbers, decimal for measured values, and date/time only for consistently recognized dates. Convert blank values to database NULL where appropriate.
6. Define primary keys and indexes required by the application. Choose whether destination tables are recreated or whether rows are appended.
7. Run the conversion, then open the result with SQL Server Compact Toolbox or the target application. Check table names, column types, row counts, keys, indexes, null values, dates, and representative records.

For a controlled free workflow, export each relevant worksheet with File → Save As → CSV UTF-8, create an SQL Server Compact database with a compatible administration tool, and import the CSV data using a compatible SQL Server Compact utility. CSV preserves values only; it does not preserve formulas, formatting, relationships, charts, or workbook metadata. SQL Server Compact Toolbox can inspect schemas and run queries, but CSV-import capabilities depend on its version and installed extensions.

If no suitable migration utility is available, a .NET program can read XLSX data with a library such as ExcelDataReader, create tables through System.Data.SqlServerCe, and insert rows with parameterized commands. This method allows explicit rules for type conversion, nulls, duplicate keys, table naming, and multiple worksheets, but requires development and a compatible SQL Server Compact provider.

Generic online converters are usually unsuitable because few support SQL Server Compact as a destination and a file named .sdf may represent different database products. Do not upload confidential workbooks unless the service explicitly documents SQL Server Compact output, retention, and deletion policies.

Quality and compatibility limits

• Most importers transfer a formula's cached result rather than its Excel formula. Recalculate and save the workbook first if the cached values are needed; database queries will not reproduce Excel formulas.
• Formatting, charts, comments, conditional formatting, macros, merged cells, and workbook-level names have no direct relational equivalent and are normally discarded.
• Excel columns can contain mixed types, while an SQL Server Compact column has one defined type. Inspect ambiguous columns before conversion; importing uncertain values as text is safer than silently losing them.
• Excel dates may be serial numbers or locale-dependent text. Verify day/month ordering, date-system handling, time zones, and conversion of blank dates to SQL NULL.
• Spaces, punctuation, reserved words, and duplicate headers can cause renamed or rejected columns. Preserve a schema mapping if application code depends on exact field names.
• SQL Server Compact has engine-specific limits for database size, columns, data types, indexes, and SQL features. Large or highly relational workbooks may need several related tables or migration to a maintained database engine.
• Renaming an XLSX file, another database, or any unrelated file to .sdf does not convert it. The output must be created by SQL Server Compact software and must match the provider expected by the receiving application.