fetch(7)

1FETCH()                          SQL Commands                          FETCH()
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NAME

6       FETCH - retrieve rows from a query using a cursor
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SYNOPSIS

10       FETCH [ direction { FROM | IN } ] cursorname
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12       where direction can be empty or one of:
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14           NEXT
15           PRIOR
16           FIRST
17           LAST
18           ABSOLUTE count
19           RELATIVE count
20           count
21           ALL
22           FORWARD
23           FORWARD count
24           FORWARD ALL
25           BACKWARD
26           BACKWARD count
27           BACKWARD ALL
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DESCRIPTION

31       FETCH retrieves rows using a previously-created cursor.
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33       A cursor has an associated position, which is used by FETCH. The cursor
34       position can be before the first row of the query result, on  any  par‐
35       ticular  row  of  the result, or after the last row of the result. When
36       created, a cursor is positioned before the first row.   After  fetching
37       some rows, the cursor is positioned on the row most recently retrieved.
38       If FETCH runs off the end of the available rows then the cursor is left
39       positioned  after  the  last  row,  or before the first row if fetching
40       backward. FETCH ALL or FETCH BACKWARD ALL will always leave the  cursor
41       positioned after the last row or before the first row.
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43       The  forms  NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE fetch a single
44       row after moving the cursor appropriately. If there is no such row,  an
45       empty  result is returned, and the cursor is left positioned before the
46       first row or after the last row as appropriate.
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48       The forms using FORWARD and BACKWARD retrieve the indicated  number  of
49       rows  moving  in  the forward or backward direction, leaving the cursor
50       positioned on the last-returned row (or after/before all rows,  if  the
51       count exceeds the number of rows available).
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53       RELATIVE  0, FORWARD 0, and BACKWARD 0 all request fetching the current
54       row without moving the cursor, that is, re-fetching the  most  recently
55       fetched  row.  This will succeed unless the cursor is positioned before
56       the first row or after the last row; in which case, no row is returned.
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PARAMETERS

59       direction
60              direction defines the fetch direction  and  number  of  rows  to
61              fetch. It can be one of the following:
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63              NEXT   Fetch  the  next row. This is the default if direction is
64                     omitted.
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66              PRIOR  Fetch the prior row.
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68              FIRST  Fetch the first row of the query (same as ABSOLUTE 1).
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70              LAST   Fetch the last row of the query (same as ABSOLUTE -1).
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72              ABSOLUTE count
73                     Fetch the count'th row of the query, or the abs(count)'th
74                     row  from  the  end if count is negative. Position before
75                     first row or after last row if count is out of range;  in
76                     particular, ABSOLUTE 0 positions before the first row.
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78              RELATIVE count
79                     Fetch  the  count'th succeeding row, or the abs(count)'th
80                     prior row if count is negative. RELATIVE 0 re-fetches the
81                     current row, if any.
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83              count  Fetch the next count rows (same as FORWARD count).
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85              ALL    Fetch all remaining rows (same as FORWARD ALL).
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87              FORWARD
88                     Fetch the next row (same as NEXT).
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90              FORWARD count
91                     Fetch the next count rows.  FORWARD 0 re-fetches the cur‐
92                     rent row.
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94              FORWARD ALL
95                     Fetch all remaining rows.
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97              BACKWARD
98                     Fetch the prior row (same as PRIOR).
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100              BACKWARD count
101                     Fetch the prior count rows (scanning backwards). BACKWARD
102                     0 re-fetches the current row.
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104              BACKWARD ALL
105                     Fetch all prior rows (scanning backwards).
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107       count  count  is  a  possibly-signed  integer constant, determining the
108              location or number of rows to fetch. For  FORWARD  and  BACKWARD
109              cases, specifying a negative count is equivalent to changing the
110              sense of FORWARD and BACKWARD.
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112       cursorname
113              An open cursor's name.
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OUTPUTS

116       On successful completion, a FETCH command returns a command tag of  the
117       form
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119       FETCH count
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121       The  count  is the number of rows fetched (possibly zero). Note that in
122       psql, the command tag will not actually be displayed, since  psql  dis‐
123       plays the fetched rows instead.
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NOTES

126       The  cursor should be declared with the SCROLL option if one intends to
127       use any variants of FETCH other than FETCH NEXT or FETCH FORWARD with a
128       positive  count.  For  simple  queries  PostgreSQL will allow backwards
129       fetch from cursors not declared with SCROLL, but this behavior is  best
130       not  relied  on.  If the cursor is declared with NO SCROLL, no backward
131       fetches are allowed.
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133       ABSOLUTE fetches are not any faster than navigating to the desired  row
134       with  a  relative move: the underlying implementation must traverse all
135       the intermediate rows  anyway.   Negative  absolute  fetches  are  even
136       worse: the query must be read to the end to find the last row, and then
137       traversed backward from there. However, rewinding to the start  of  the
138       query (as with FETCH ABSOLUTE 0) is fast.
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140       Updating data via a cursor is currently not supported by PostgreSQL.
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142       DECLARE  [declare(7)] is used to define a cursor. Use MOVE [move(7)] to
143       change cursor position without retrieving data.
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EXAMPLES

146       The following example traverses a table using a cursor.
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148       BEGIN WORK;
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150       -- Set up a cursor:
151       DECLARE liahona SCROLL CURSOR FOR SELECT * FROM films;
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153       -- Fetch the first 5 rows in the cursor liahona:
154       FETCH FORWARD 5 FROM liahona;
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156        code  |          title          | did | date_prod  |   kind   |  len
157       -------+-------------------------+-----+------------+----------+-------
158        BL101 | The Third Man           | 101 | 1949-12-23 | Drama    | 01:44
159        BL102 | The African Queen       | 101 | 1951-08-11 | Romantic | 01:43
160        JL201 | Une Femme est une Femme | 102 | 1961-03-12 | Romantic | 01:25
161        P_301 | Vertigo                 | 103 | 1958-11-14 | Action   | 02:08
162        P_302 | Becket                  | 103 | 1964-02-03 | Drama    | 02:28
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164       -- Fetch the previous row:
165       FETCH PRIOR FROM liahona;
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167        code  |  title  | did | date_prod  |  kind  |  len
168       -------+---------+-----+------------+--------+-------
169        P_301 | Vertigo | 103 | 1958-11-14 | Action | 02:08
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171       -- Close the cursor and end the transaction:
172       CLOSE liahona;
173       COMMIT WORK;
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COMPATIBILITY

177       The SQL standard defines FETCH for use in embedded SQL only. The  vari‐
178       ant  of  FETCH  described  here returns the data as if it were a SELECT
179       result rather than placing it in host variables. Other than this point,
180       FETCH is fully upward-compatible with the SQL standard.
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182       The  FETCH  forms  involving FORWARD and BACKWARD, as well as the forms
183       FETCH count and FETCH ALL, in which FORWARD is implicit, are PostgreSQL
184       extensions.
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186       The SQL standard allows only FROM preceding the cursor name; the option
187       to use IN is an extension.
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