SQLite Default Values Not Applied When Inserting via GUI Tool: Causes and Fixes

Schema Design, Default Constraints, and Insertion Method Interactions

The core issue revolves around default column values not being applied when inserting records through a third-party GUI tool (SQLiteStudio) while functioning as expected via a custom application. This discrepancy stems from interactions between SQLite’s default value handling, schema design choices, and differences in how insertion commands are structured by different clients.

Key Elements of the Problem

1. Column Definitions with Implicit Type Affinity:
   The table uses BOOLEAN declarations, which SQLite does not natively support. SQLite employs type affinity, where BOOLEAN is not a distinct type but resolves to NUMERIC affinity. This can lead to unexpected behavior when values are inserted as NULL instead of being omitted, bypassing default value assignment.

2. Default Value Application Rules:
   SQLite applies default values only when a column is not specified in the INSERT statement or is explicitly assigned DEFAULT. If an insertion includes the column with a NULL value (even implicitly), the default is not applied.

3. Tool-Specific Insertion Logic:
   GUI tools like SQLiteStudio may generate INSERT statements that include all columns, explicitly setting NULL for fields left "empty" in their interface. This bypasses SQLite’s default value mechanism.

4. Missing NOT NULL Constraints:
   Columns declared with DEFAULT but without NOT NULL allow explicit NULL assignments, which override defaults.

Root Causes: Why Defaults Fail in GUI Tools but Work in Applications

1. Type Affinity Mismatch and Implicit NULLs

The schema declares BOOLEAN columns, which SQLite treats as NUMERIC (effectively INTEGER). However, GUI tools may interpret "empty" boolean fields as NULL rather than omitting them. For example:

• Application Insert: Omits bLabelPrinted, triggering the default 0.
• SQLiteStudio Insert: Includes bLabelPrinted with NULL, stored as-is.

Example of problematic insertion from SQLiteStudio:

INSERT INTO tblMailingList (..., bLabelPrinted, ...) VALUES (..., NULL, ...);

This explicitly assigns NULL instead of relying on the default.

2. Default Value Activation Conditions

SQLite’s DEFAULT clause activates under two conditions:

• The column is absent from the INSERT column list.
• The DEFAULT keyword is used in the VALUES clause.

Most GUI tools generate INSERT statements that include all columns, even those left blank. If the tool populates "empty" fields as NULL, defaults are bypassed.

3. AUTOINCREMENT and Schema Redundancy

The iMailingListID column is declared as:

INTEGER PRIMARY KEY AUTOINCREMENT UNIQUE NOT NULL

This introduces unnecessary redundancy:

• INTEGER PRIMARY KEY already implies UNIQUE and NOT NULL.
• AUTOINCREMENT is rarely needed and imposes overhead by preventing ROWID reuse.
  While not directly causing the default value issue, this reflects broader schema design inconsistencies that could affect data integrity.

Resolving the Issue: Schema Adjustments, Tool Configuration, and Insertion Patterns

1. Revise Column Definitions to Enforce Defaults

Modify BOOLEAN columns to explicitly use INTEGER affinity with NOT NULL and DEFAULT constraints:

ALTER TABLE tblMailingList RENAME TO tmp_tblMailingList;

CREATE TABLE tblMailingList (
  iMailingListID INTEGER PRIMARY KEY,  -- Remove AUTOINCREMENT unless strictly required
  -- ... other columns ...
  bLabelPrinted INTEGER NOT NULL DEFAULT 0 CHECK (bLabelPrinted IN (0, 1)),
  bToBePrinted INTEGER NOT NULL DEFAULT 0 CHECK (bToBePrinted IN (0, 1)),
  bBlankRecord INTEGER NOT NULL DEFAULT 0 CHECK (bBlankRecord IN (0, 1))
);

INSERT INTO tblMailingList SELECT * FROM tmp_tblMailingList;
DROP TABLE tmp_tblMailingList;

• NOT NULL: Prevents explicit NULL assignments.
• CHECK: Enforces boolean semantics (0/1).
• DEFAULT 0: Ensures the default is applied when the column is omitted.

If existing data contains NULL in these columns, use COALESCE during migration:

INSERT INTO tblMailingList 
SELECT 
  iMailingListID,
  sFirstName,
  sLastName,
  sSpouseName,
  sAddressLine1,
  sAddressLine2,
  sCity,
  sState,
  sPostalCode,
  sLandLinePhone,
  sMobilePhone,
  sEmailAddress,
  COALESCE(bLabelPrinted, 0),
  COALESCE(bToBePrinted, 0),
  COALESCE(bBlankRecord, 0)
FROM tmp_tblMailingList;

2. Configure SQLiteStudio to Omit NULL Columns

Adjust the GUI tool’s behavior to exclude columns with NULL values from INSERT statements:

• Option 1: Use the DEFAULT keyword in manual inserts:

  INSERT INTO tblMailingList (..., bLabelPrinted, ...) 
  VALUES (..., DEFAULT, ...);
  

• Option 2: In SQLiteStudio’s table editor:
  1. Right-click the table > Edit Table.
  2. Navigate to Columns tab.
  3. For each boolean column, check "Not Null" and set Default Value to 0.
  4. Ensure the "Insert NULL for empty values" option is disabled in preferences.

3. Use Triggers as a Fallback

If modifying the tool’s behavior is impractical, create BEFORE INSERT triggers to replace NULL with defaults:

CREATE TRIGGER trg_tblMailingList_bLabelPrinted 
BEFORE INSERT ON tblMailingList 
WHEN NEW.bLabelPrinted IS NULL 
BEGIN
  UPDATE tblMailingList SET bLabelPrinted = 0 WHERE rowid = NEW.rowid;
END;

Repeat for other boolean columns.

4. Audit AUTOINCREMENT Usage

Remove AUTOINCREMENT unless strictly required for ROWID monotonicity across deletions:

CREATE TABLE tblMailingList (
  iMailingListID INTEGER PRIMARY KEY,  -- AUTOINCREMENT removed
  -- ... other columns ...
);

This reduces overhead and avoids sqlite_sequence table maintenance.

Summary of Fixes and Best Practices

1. Explicit Column Typing: Use INTEGER instead of BOOLEAN with CHECK constraints for boolean logic.
2. Enforce Non-Nullability: Add NOT NULL to columns with defaults to prevent NULL overrides.
3. Tool Configuration: Ensure GUI tools omit columns or use DEFAULT instead of inserting NULL.
4. Schema Simplification: Remove redundant constraints like AUTOINCREMENT unless explicitly required.

By aligning schema design with SQLite’s type affinity rules and understanding how insertion methods interact with default constraints, the inconsistency between application and GUI tool behavior can be fully resolved.