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- Constraints 13413
- In SQL, constraints can be specified for tables. Constraints enforce certain properties over data that is inserted into a table. Constraints can be specified along with the schema of the table as part of the CREATE TABLE statement . In cert
...rbitrary Boolean expression. Any columns that do not satisfy this expression violate the constraint. For example, we could enforce that the name column does not contain spaces using the following CHECK constraint. CREATE TABLE students (name VARCHAR CHE...umn cannot contain any NULL values. By default, all columns in tables are nullable. Adding NOT NULL to a column definition enforces that a column cannot contain NULL values. CREATE TABLE students (name VARCHAR NOT NULL); INSERT INTO students VALUES (NUL...unique constraints define a column, or set of columns, that are a unique identifier for a row in the table. The constraint enforces that the specified columns are unique within a table, i.e., that at most one row contains the given values for the set of... - https://man.mtool.work/duckdb/2.0/sql/constraints.html
- Non-Deterministic Behavior 8869
- Several operators in DuckDB exhibit non-deterministic behavior. Most notably, SQL uses set semantics, which allows results to be returned in a different order. DuckDB exploits this to improve performance, particularly when performing multi-
...ng workarounds: Limit the number of threads to prevent non-determinism introduced by multi-threading. sql SET threads = 1; Enforce ordering. For example, you can use the ORDER BY ALL clause : sql SELECT * FROM ( SELECT 'A' AS x UNION SELECT 'B' AS x ) O... - https://man.mtool.work/duckdb/2.0/operations_manual/non-deterministic_behavior.h...
- Comparisons 8869
- Comparison Operators The table below shows the standard comparison operators. Whenever either of the input arguments is NULL , the output of the comparison is NULL . Operator Description Example Result < less than 2 < 3 true > greater than
...ssions evaluate and return true in DuckDB but fail in PostgreSQL. SELECT 1 = true; SELECT 1 = '1.1'; It is not possible to enforce stricter type-checking for DuckDB's comparison operators. If you require stricter type-checking, consider creating a macro... - https://man.mtool.work/duckdb/2.0/sql/expressions/comparison_operators.html
- Securing Extensions 8433
- DuckDB has a powerful extension mechanism, which has the same privileges as the user running DuckDB's (parent) process. This introduces security considerations. Therefore, we recommend reviewing the configuration options listed on this page
..., and routinely install a staggering amount of transitive dependencies without thinking twice. Some repositories like CRAN enforce a human inspection at some point, but that's no guarantee for anything either. We've studied several different approaches... - https://man.mtool.work/duckdb/2.0/operations_manual/securing_duckdb/securing_ext...
- Excel Extension 8215
- The excel extension provides functions to format numbers per Excel's formatting rules by wrapping the i18npool library and to read/write Excel ( .xlsx ) files. However, please note that .xls files are not supported. Installing and Loading T
...CT * FROM test; Type and Range Inference Because Excel itself only really stores numbers or strings in cells, and does not enforce that all cells in a column are of the same type, the excel extension has to do some guesswork to "infer" and decide the ty... - https://man.mtool.work/duckdb/2.0/core_extensions/excel.html
- Enum Data Type 8215
- Name Description ENUM Dictionary representing all possible string values of a column The enum type represents a dictionary data structure with all possible unique values of a column. For example, a column storing the days of the week can be
...WHERE current_mood = 'bogus'; -- Equivalent to `WHERE current_mood::VARCHAR = 'bogus'` -- No rows returned If you want to enforce type-safety, cast to the enum explicitly: SELECT * FROM person WHERE current_mood = 'bogus'::mood; -- Conversion Error: Co... - https://man.mtool.work/duckdb/2.0/sql/data_types/enum.html
- DuckDB_% Metadata Functions 7561
- DuckDB offers a collection of table functions that provide metadata about the current database. These functions reside in the main schema and their names are prefixed with duckdb_ . The resultset returned by a duckdb_ table function may be
...id The internal identifier of the column data type. BIGINT character_maximum_length Always NULL . DuckDB text types do not enforce a value length restriction based on a length type parameter. INTEGER numeric_precision The number of units (in the base in... - https://man.mtool.work/duckdb/2.0/sql/meta/duckdb_table_functions.html
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