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fix(mssql,oracle): render bare Stddev as sample standard deviation - #12161
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deepyaman merged 8 commits intoOct 18, 2026
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…ddev-sample # Conflicts: # ibis/backends/sql/tests/test_compiler.py
…ddev-sample # Conflicts: # ibis/backends/tests/test_dot_sql.py
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Two minor comments, and then it looks good
Co-authored-by: Deepyaman Datta <deepyaman.datta@utexas.edu>
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Description of changes
The MSSQL dialect mapped a bare
sge.StddevtoSTDEVP, but T-SQL'sSTDEVis the sample standard deviation, soSTDEVin user SQL was silently turned into a population one. Oracle had the same problem:STDDEVbecameSTDDEV_POP, even though Oracle'sSTDDEVis sample. This shows up throughTable.sql()andcon.sql(..., dialect=...), notBackend.sql()without a dialect. It also affected cross-dialect queries, e.g. a DuckDB or PostgresSTDDEVsent to MSSQL or Oracle came back as the population value.This removes the
sge.Stddevoverrides for MSSQL and Oracle, so sqlglot's defaults are used, which already renderSTDEVandSTDDEV. Since the Oracle override was applied to sqlglot's global Oracle dialect, removing it also fixes plainsqlglot.transpile(..., write="oracle")for anyone who imported ibis. SQL generated from ibis expressions liket.x.std()doesn't change, since that always goes throughstddev_samp/stddev_pop.Tests:
test_dot_sql_transpile_stddevintest_dot_sql.pyruns DuckDB SQL over a few rows on every backend and compares against the sample standard deviation (with markers for SQLite, Druid, RisingWave and BigQuery, where the query can't run as written).MySQL isn't changed here. sqlglot parses MySQL's
STDDEV/VARIANCE(population) into the same nodes as DuckDB's sample versions, so fixing that needs a change in sqlglot (tobymao/sqlglot#8626). MySQL and SingleStoreDB are markednotyetin the new test for now.Issues closed