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The DEFAULT clause specifies a default value to use for the column if no value is explicitly provided by the user when doing an INSERT.
If there is no explicit DEFAULT clause attached to a column definition, then the default value of the column is NULL.
Tables created using CREATE TABLE AS are initially populated with the rows of data returned by the SELECT statement.
However, if the "IF NOT EXISTS" clause is specified as part of the CREATE TABLE statement and a table or view of the same name already exists, the CREATE TABLE command simply has no effect (and no error message is returned).The name of each column is the same as the name of the corresponding column in the result set of the SELECT statement.The declared type of each column is determined by the expression affinity of the corresponding expression in the result set of the SELECT statement, as follows: A table created using CREATE TABLE AS has no PRIMARY KEY and no constraints of any kind. The default collation sequence for each column of the new table is BINARY.For CURRENT_TIME, the format of the value is "HH: MM: SS". The format for CURRENT_TIMESTAMP is "YYYY-MM-DD HH: MM: SS".
The COLLATE clause specifies the name of a collating sequence to use as the default collation sequence for the column.For the purposes of the DEFAULT clause, an expression is considered constant if it does contains no sub-queries, column or table references, bound parameters, or string literals enclosed in double-quotes instead of single-quotes.