ST_MakePolygon
ST_MakePolygon has two variants that return a polygon. One takes a single geometry, and another takes two geometries.
The input of the first variant is a linestring that defines the outer ring of the output polygon.
The input of the second variant is a linestring and a multilinestring. Both of these are empty or closed.
The boundary of the exterior ring of the output polygon is the input linestring, and the boundaries of the interior rings of the polygon are the linestrings in the input multilinestring. If the input linestring is empty, an empty polygon is returned. Empty linestrings in the multilinestring are disregarded. The spatial reference system identifier (SRID) of the resulting geometry is the common SRID of the two input geometries.
The dimension of the returned geometry is the same as that of the input geometries. The exterior ring and interior rings must of the same dimension.
Syntax
ST_MakePolygon(geom1)
ST_MakePolygon(geom1, geom2)
Arguments
 geom1

A value of data type
GEOMETRY
or an expression that evaluates to aGEOMETRY
type. The subtype must beLINESTRING
. The linestring value must be closed or empty.  geom2

A value of data type
GEOMETRY
or an expression that evaluates to aGEOMETRY
type. The subtype must beMULTILINESTRING
.
Return type
GEOMETRY
of subtype POLYGON
.
The spatial reference system identifier (SRID) of the returned geometry is equal to the SRID of the inputs.
If geom1, or geom2 is null, then null is returned.
If geom1 is not a linestring, then an error is returned.
If geom2 is not a multilinestring, then an error is returned.
If geom1 is not closed, then an error is returned.
If geom1 is a single point or is not closed, then an error is returned.
If geom2 contains at least one linestring that has a single point or is not closed, then an error is returned.
If geom1 and geom2 have different SRID values, then an error is returned.
If geom1 and geom2 have different dimensions, then an error is returned.
Examples
The following SQL returns a polygon from an input linestring.
SELECT ST_AsText(ST_MakePolygon(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)')));
st_astext

POLYGON((77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07))
The following SQL creates a polygon from a closed linestring and a closed multilinestring. The linestring is used for the exterior ring of the polygon. The linestrings in the multilinestrings are used for the interior rings of the polygon.
SELECT ST_AsEWKT(ST_MakePolygon(ST_GeomFromText('LINESTRING(0 0,10 0,10 10,0 10,0 0)'), ST_GeomFromText('MULTILINESTRING((1 1,1 2,2 1,1 1),(3 3,3 4,4 3,3 3))')));
st_astext

POLYGON((0 0,10 0,10 10,0 10,0 0),(1 1,1 2,2 1,1 1),(3 3,3 4,4 3,3 3))