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transform: coerce empty strings to NULL when converting TEXT columns to numeric types

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When a TEXT column is transformed to INTEGER, FLOAT, or REAL and a row
contains an empty string, the empty string is now converted to NULL during
the INSERT...SELECT copy, matching the expected behavior described in #488.

Fixes #488
This commit is contained in:
Claude 2026-07-18 14:50:50 +00:00
commit 58f5aeb37f
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2 changed files with 40 additions and 4 deletions
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21
sqlite_utils/db.py
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@ -2856,6 +2856,19 @@ class Table(Queryable):
).strip()
)
# Columns being changed from TEXT to a numeric type: coerce empty strings to NULL
_numeric_sql_types = {"INTEGER", "REAL", "FLOAT", "NUMERIC"}
text_to_numeric_cols = {
col_name
for col_name, new_type in types.items()
if existing_columns.get(col_name) == str
and COLUMN_TYPE_MAPPING.get(
new_type,
new_type.upper() if isinstance(new_type, str) else "",
)
in _numeric_sql_types
}
# Copy across data, respecting any renamed columns
new_cols = []
old_cols = []
@ -2866,10 +2879,16 @@ class Table(Queryable):
if "rowid" not in new_cols:
new_cols.insert(0, "rowid")
old_cols.insert(0, "rowid")
def _copy_expr(col):
if col in text_to_numeric_cols:
return "NULLIF({}, '')".format(quote_identifier(col))
return quote_identifier(col)
copy_sql = "INSERT INTO {} ({new_cols})\n SELECT {old_cols} FROM {};".format(
quote_identifier(new_table_name),
quote_identifier(self.name),
old_cols=", ".join(quote_identifier(col) for col in old_cols),
old_cols=", ".join(_copy_expr(col) for col in old_cols),
new_cols=", ".join(quote_identifier(col) for col in new_cols),
)
sqls.append(copy_sql)