PostgreSQL/Select Query/EXPLAIN Query

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A verbose explanation of a simpler query, with the VERBOSE keyword

postgres=#
postgres=# CREATE TABLE employee (
postgres(#     ID         int,
postgres(#     name       varchar(10),
postgres(#     salary     real,
postgres(#     start_date date,
postgres(#     city       varchar(10),
postgres(#     region     char(1)
postgres(# );
CREATE TABLE
postgres=#
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (1,  "Jason", 40420,  "02/01/94", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (2,  "Robert",14420,  "01/02/95", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (3,  "Celia", 24020,  "12/03/96", "Toronto",  "W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (4,  "Linda", 40620,  "11/04/97", "New York", "N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (5,  "David", 80026,  "10/05/98", "Vancouver","W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (6,  "James", 70060,  "09/06/99", "Toronto",  "N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (7,  "Alison",90620,  "08/07/00", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (8,  "Chris", 26020,  "07/08/01", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (9,  "Mary",  60020,  "06/09/02", "Toronto",  "W");
INSERT 0 1
postgres=#
postgres=# select * from employee;
 id |  name  | salary | start_date |   city    | region
----+--------+--------+------------+-----------+--------
  1 | Jason  |  40420 | 1994-02-01 | New York  | W
  2 | Robert |  14420 | 1995-01-02 | Vancouver | N
  3 | Celia  |  24020 | 1996-12-03 | Toronto   | W
  4 | Linda  |  40620 | 1997-11-04 | New York  | N
  5 | David  |  80026 | 1998-10-05 | Vancouver | W
  6 | James  |  70060 | 1999-09-06 | Toronto   | N
  7 | Alison |  90620 | 2000-08-07 | New York  | W
  8 | Chris  |  26020 | 2001-07-08 | Vancouver | N
  9 | Mary   |  60020 | 2002-06-09 | Toronto   | W
(9 rows)
postgres=#
postgres=#
postgres=#
postgres=# -- A verbose explanation of a simpler query, with the VERBOSE keyword:
postgres=#
postgres=# EXPLAIN VERBOSE SELECT * FROM employee;
                         QUERY PLAN
-------------------------------------------------------------
    {SEQSCAN
    :startup_cost 0.00
    :total_cost 20.30
    :plan_rows 1030
    :plan_width 45
    :targetlist (
       {TARGETENTRY
       :expr
          {VAR
          :varno 1
          :varattno 1
          :vartype 23
          :vartypmod -1
          :varlevelsup 0
          :varnoold 1
          :varoattno 1
          }
       :resno 1
       :resname id
       :ressortgroupref 0
       :resorigtbl 19576
       :resorigcol 1
       :resjunk false
       }
       {TARGETENTRY
       :expr
          {VAR
          :varno 1
          :varattno 2
          :vartype 1043
          :vartypmod 14
          :varlevelsup 0
          :varnoold 1
          :varoattno 2
          }
       :resno 2
       :resname name
       :ressortgroupref 0
       :resorigtbl 19576
       :resorigcol 2
       :resjunk false
       }
       {TARGETENTRY
       :expr
          {VAR
          :varno 1
          :varattno 3
          :vartype 700
          :vartypmod -1
          :varlevelsup 0
          :varnoold 1
          :varoattno 3
          }
       :resno 3
       :resname salary
       :ressortgroupref 0
       :resorigtbl 19576
       :resorigcol 3
       :resjunk false
       }
       {TARGETENTRY
       :expr
          {VAR
          :varno 1
          :varattno 4
          :vartype 1082
          :vartypmod -1
          :varlevelsup 0
          :varnoold 1
          :varoattno 4
          }
       :resno 4
       :resname start_date
       :ressortgroupref 0
       :resorigtbl 19576
       :resorigcol 4
       :resjunk false
       }
       {TARGETENTRY
       :expr
          {VAR
          :varno 1
          :varattno 5
          :vartype 1043
          :vartypmod 14
          :varlevelsup 0
          :varnoold 1
          :varoattno 5
          }
       :resno 5
       :resname city
       :ressortgroupref 0
       :resorigtbl 19576
       :resorigcol 5
       :resjunk false
       }
       {TARGETENTRY
       :expr
          {VAR
          :varno 1
          :varattno 6
          :vartype 1042
          :vartypmod 5
          :varlevelsup 0
          :varnoold 1
          :varoattno 6
          }
       :resno 6
       :resname region
       :ressortgroupref 0
       :resorigtbl 19576
       :resorigcol 6
       :resjunk false
       }
    )
    :qual <>
    :lefttree <>
    :righttree <>
    :initPlan <>
    :extParam (b)
    :allParam (b)
    :nParamExec 0
    :scanrelid 1
    }
 Seq Scan on employee  (cost=0.00..20.30 rows=1030 width=45)
(126 rows)
postgres=#



Executing EXPLAIN for a query

postgres=#
postgres=# CREATE TABLE employee (
postgres(#     ID         int,
postgres(#     name       varchar(10),
postgres(#     salary     real,
postgres(#     start_date date,
postgres(#     city       varchar(10),
postgres(#     region     char(1)
postgres(# );
ERROR:  relation "employee" already exists
postgres=#
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (1,  "Jason", 40420,  "02/01/94", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (2,  "Robert",14420,  "01/02/95", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (3,  "Celia", 24020,  "12/03/96", "Toronto",  "W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (4,  "Linda", 40620,  "11/04/97", "New York", "N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (5,  "David", 80026,  "10/05/98", "Vancouver","W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (6,  "James", 70060,  "09/06/99", "Toronto",  "N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (7,  "Alison",90620,  "08/07/00", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (8,  "Chris", 26020,  "07/08/01", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name,    salary, start_date, city,       region)
postgres-#               values (9,  "Mary",  60020,  "06/09/02", "Toronto",  "W");
INSERT 0 1
postgres=#
postgres=# select * from employee;
 id |  name  | salary | start_date |   city    | region
----+--------+--------+------------+-----------+--------
  1 | Jason  |  40420 | 1994-02-01 | New York  | W
  2 | Robert |  14420 | 1995-01-02 | Vancouver | N
  3 | Celia  |  24020 | 1996-12-03 | Toronto   | W
  4 | Linda  |  40620 | 1997-11-04 | New York  | N
  5 | David  |  80026 | 1998-10-05 | Vancouver | W
  6 | James  |  70060 | 1999-09-06 | Toronto   | N
  7 | Alison |  90620 | 2000-08-07 | New York  | W
  8 | Chris  |  26020 | 2001-07-08 | Vancouver | N
  9 | Mary   |  60020 | 2002-06-09 | Toronto   | W
  1 | Jason  |  40420 | 1994-02-01 | New York  | W
  2 | Robert |  14420 | 1995-01-02 | Vancouver | N
  3 | Celia  |  24020 | 1996-12-03 | Toronto   | W
  4 | Linda  |  40620 | 1997-11-04 | New York  | N
  5 | David  |  80026 | 1998-10-05 | Vancouver | W
  6 | James  |  70060 | 1999-09-06 | Toronto   | N
  7 | Alison |  90620 | 2000-08-07 | New York  | W
  8 | Chris  |  26020 | 2001-07-08 | Vancouver | N
  9 | Mary   |  60020 | 2002-06-09 | Toronto   | W
(18 rows)
postgres=#
postgres=# -- Executing EXPLAIN for a query
postgres=#
postgres=# EXPLAIN SELECT * FROM employee;
                         QUERY PLAN
-------------------------------------------------------------
 Seq Scan on employee  (cost=0.00..20.30 rows=1030 width=45)
(1 row)
postgres=#
postgres=# drop table employee;
DROP TABLE
postgres=#
postgres=#
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