The SYS_COLUMNS table lists the columns of the tables and their parameters. The columns of a collection are the fields of its first documents (Describe Amount) and the fields of its schema validator, as the queries of the connection see them. It has the following columns:

Column Name	Data Type	Description
TABLE_CATALOG	VARCHAR	The name of the database of the connection.
TABLE_SCHEMA	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
TABLE_NAME	VARCHAR	The name of the collection or view which the column belongs to.
COLUMN_NAME	VARCHAR	The name of the column: the name of the field; a field of an embedded document or an element of an array has a dotted name (address.city, tags.0). When field names differ only in case, the column of the second spelling has a suffix (name_1).
ORDINAL_POSITION	INT	The position of the column in the table.
IS_NULLABLE	VARCHAR	Indicates whether this column can be NULL ("YES" or "NO"). "NO" for _id and for a NOT NULL column of a collection whose documents MongoDB checks (Schema Validation=Error).
COLUMN_DEFAULT	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
DATA_TYPE	VARCHAR	The data type of the column, for example OID, VARCHAR, INT, DOUBLE, DATETIME. A column created with CREATE TABLE has the type its values are stored and read as: SMALLINT stays SMALLINT, DECIMAL(5,2) gives DOUBLE.
CHARACTER_MAXIMUM_LENGTH	INT	The maximum length of the column in characters: n for a column declared as CHAR(n), NCHAR(n), VARCHAR(n) or NVARCHAR(n). NULL for other columns.
CHARACTER_OCTET_LENGTH	INT	Not used in dotConnect for MongoDB. Always NULL.
NUMERIC_PRECISION	INT	The precision of numeric data: p for a column declared as DECIMAL(p,s) or NUMERIC(p,s). NULL for other columns.
NUMERIC_PRECISION_RADIX	INT	The precision radix of numeric data: 10 for a column declared as DECIMAL(p,s) or NUMERIC(p,s). NULL for other columns.
NUMERIC_SCALE	INT	The scale of numeric data: s for a column declared as DECIMAL(p,s) or NUMERIC(p,s). NULL for other columns.
DATETIME_PRECISION	INT	Not used in dotConnect for MongoDB. Always NULL.
CHARACTER_SET_CATALOG	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
CHARACTER_SET_SCHEMA	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
CHARACTER_SET_NAME	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
COLLATION_CATALOG	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
COLLATION_SCHEMA	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
COLLATION_NAME	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
DOMAIN_CATALOG	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
DOMAIN_SCHEMA	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
DOMAIN_NAME	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
ALLOWED_OPERATIONS	INT	Contains flag value that indicates which DML operations are allowed on this column and is the sum of the following flags: 1 - INSERT operations are allowed 2 - UPDATE operations are allowed 3 for a column of a collection, 0 for a column of a view.
HAS_DEFAULT	BOOLEAN	Indicates whether the column has the default value. Always False.
IS_COMPUTED	BOOLEAN	Indicates whether the column is computed. Always False.
IS_UNIQUE	BOOLEAN	Indicates whether the column must have unique values: True for _id and for a field that has a unique index on this field alone without a filter (partialFilterExpression).
DB_TYPE	INT	Numeric representation of the DbType value.
NATIVE_TYPE	INT	Numeric representation of the MongoDBType value.
API_NAME	VARCHAR	The name of the field in MongoDB. Differs from COLUMN_NAME for a column with a suffix (name for name_1).
IS_REQUIRED	VARCHAR	"YES" for _id and for a field the schema validator requires (a NOT NULL column of CREATE TABLE), whatever the validation level; "NO" otherwise.
IS_HIDDEN	BOOLEAN	Indicates whether the column is hidden: SELECT * does not return it, but a query may name it. The whole value of a Binary, Timestamp, regular expression or JavaScript field that is also split into part columns (ts for ts.t and ts.i), and the fields inside a JSON column (Json Fields, Complex As String) are hidden.
SOURCE	VARCHAR	Where the column comes from: "sample" - the documents read have the field; "validator" - only the schema validator declares it; "both" - both; "model" - neither, the column comes from the Entity Framework Core model.