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Parse the SELECT clause of an EK query, returning full particulars concerning each selected item.
None.
Variable I/O Description -------- --- -------------------------------------------------- query I EK query. msglen I Available space in the output error message string. n O Number of items in SELECT clause of query. xbegs O Begin positions of expressions in SELECT clause. xends O End positions of expressions in SELECT clause. xtypes O Data types of expressions. xclass O Classes of expressions. tabs O Names of tables qualifying SELECT columns. cols O Names of columns in SELECT clause of query. error O Error flag. errmsg O Parse error message.
query is a character string containing an EK query.
EK queries have the general form
SELECT <select expr>, <select expr>, ...
FROM <table spec>, <table spec>, ...
[WHERE <constraint list>]
[ORDER BY <order-by column list>]
Here the symbol <select expr> indicates any
expression representing an entity that can be
selected. Commonly, the selected items are
columns, with or without qualifying table names,
having the form
<column name>
<table name>.<column name>
<table alias>.<column name>
but more general expressions may also be selected.
Examples are functions, such as
COUNT(*)
COUNT( <table name>.<column name> )
MAX ( <table name>.<column name> )
or expressions involving constants, such as
2 * <column name>
msglen The allowed length for the output message string.
This length must large enough to hold the output
string plus the terminator. If the output string is
expected to have x characters, msglen needs to be
x + 1.
tablen The length of the strings in the output table array.
This length must large enough to hold the output
strings plus the terminator. If the output strings
are expected to have x characters, tablen needs to be
x + 1. The parameter SPICE_EK_TSTRLN defines a string
length sufficient to hold any table name. This
parameter is defined by SpiceUsr.h.
collen The length of the strings in the output column array.
This length must large enough to hold the output
strings plus the terminator. If the output strings
are expected to have x characters, collen needs to be
x + 1. The parameter SPICE_EK_CSTRLN defines a string
length sufficient to hold any table name. This
parameter is defined by SpiceUsr.h.
n is the number of items specified in the
SELECT clause of the input query.
xbegs,
xends are, respectively, arrays of begin and end
positions of expressions designating items in the
SELECT clause of the input query. The ith
expression is located in the substring
query[ xbegs[i] ]...query[ xends[i] ]
xtypes is an array of values of type SpiceEKDataType giving
types of the expressions in the SELECT clause.
Values and meanings of xtypes are:
SPICE_CHR Character type
SPICE_DP Double precision type
SPICE_INT Integer type
SPICE_TIME Time type
The ith element of xtypes refers to the ith
selected item.
The data type of an expression indicates which
fetch routine to use to obtain values of the
selected expression. The mapping of data types
to fetch routines is shown below:
SPICE_CHR ekgc_c
SPICE_DP ekgd_c
SPICE_INT ekgi_c
SPICE_TIME ekgd_c
Note that time values are stored as d.p. numbers.
xclass is an array of values of type SpiceEKExprClass giving
the classes of the expressions occurring in the SELECT
clause of the input query. Values and meanings of
xclass are:
SPICE_EK_EXP_COL Selected item was a column.
The column may qualified by a
table name.
SPICE_EK_EXP_FUNC Selected item was a simple
function invocation of the
form
F ( <column> )
or else was
COUNT(*)
SPICE_EK_EXP_EXPR Selected item was a more
general expression than those
shown above.
The Ith element of xclass refers to the Ith
selected item.
When a selected item is a column, the values of
the arguments tabs and cols (discussed below) are
defined.
tabs is an array of names of tables corresponding to
the columns in the SELECT clause. The ith element
of tabs corresponds to the table containing the
ith SELECT column. Table names returned in tabs
are the actual names of tables in loaded EKs, not
aliases supplied in the input query. Table names
are supplied even if the corresponding column was
unqualified in the input query, as long as the
column name was unambiguous.
The contents of tabs[i] are defined if and only if
the returned value of xclass[i] is SPICE_EK_EXP_COL.
cols is an array containing the columns of the SELECT
clause. The contents of cols[i] are defined if and
only if the returned value of xclass[i] is
SPICE_EK_EXP_COL.
error is a logical flag indicating whether the input
query parsed correctly. The other outputs of this
routine, except for errmsg, are undefined if a
parse error occurred. error is returned SPICETRUE if
a parse error occurred, SPICEFALSE otherwise.
errmsg is a character string describing the cause of a
parse error, if such an error occurred. Otherwise,
errmsg is returned empty.
None.
This routine allows callers of the EK fetch routines to determine at run time the attributes of the columns from which data is to be fetched.
1) Use of ekpsel_c to assist in fetching rows matching queries
supplied at run time.
The code fragment shown here does not rely on advance
knowledge of the input query or the contents of any loaded EK
files.
To simplify the example, we assume that all columns are scalar-
valued.
#include "SpiceUsr.h"
#include <stdio.h>
#include <string.h>
void main()
{
/.
The kernel names that appear here are examples; to use this
program, you would have to replace these names with those of
kernels available on your own system.
./
#define EK "/kernels/galileo/ek/EK97148A.BSE"
#define LSK "/kernels/gen/lsk/leapseconds.ker"
#define MSGLEN 320
#define LNSIZE 80
#define TIMELEN 25
SpiceBoolean error;
SpiceBoolean found;
SpiceBoolean null;
SpiceChar cdata [LNSIZE];
SpiceChar cols [SPICE_EK_MAXQSEL]
[SPICE_EK_CSTRLN];
SpiceChar errmsg [MSGLEN];
SpiceChar outstr [LNSIZE];
SpiceChar * query;
SpiceChar tabs [SPICE_EK_MAXQSEL]
[SPICE_EK_TSTRLN];
SpiceChar utc [TIMELEN];
SpiceDouble ddata;
SpiceDouble tdata;
SpiceEKDataType xtypes [SPICE_EK_MAXQSEL];
SpiceEKExprClass xclass [SPICE_EK_MAXQSEL];
SpiceInt col;
SpiceInt exprlen;
SpiceInt handle;
SpiceInt idata;
SpiceInt n;
SpiceInt nmrows;
SpiceInt row;
SpiceInt xbegs [SPICE_EK_MAXQSEL];
SpiceInt xends [SPICE_EK_MAXQSEL];
/.
Load leapseconds and E-kernels.
./
ldpool_c ( LSK );
eklef_c ( EK, &handle );
while ( SPICETRUE )
{
/.
Prompt for query. Parse the SELECT clause using ekpsel_c.
./
query = prompt_c ( "Enter query > " );
ekpsel_c ( query,
MSGLEN,
&n,
xbegs,
xends,
xtypes,
xclass,
tabs,
cols,
&error,
errmsg );
if ( error )
{
printf ( "Error: <%s>\n", errmsg );
}
else
{
/.
Submit query to the EK query system.
./
ekfind_c ( query, MSGLEN, &nmrows, &error, errmsg );
if ( error )
{
printf ( "Error found: %s\n", errmsg );
}
else
{
printf ( "Number of matching rows = %d\n", nmrows );
/.
Fetch the rows that matched the query.
./
for ( row = 0; row < nmrows; row++ )
{
/.
Fetch data from the current row.
./
printf ( "\nROW = %d\n", row );
for ( col = 0; col < n; col++ )
{
/.
Fetch data from the current selected column.
./
if ( xclass[col] == SPICE_EK_EXP_COL )
{
printf ( "COLUMN = %s.%s\n",
tabs[col],
cols[col] );
}
else
{
exprlen = xends[col] - xbegs[col] + 1;
strncpy ( outstr, query+xbegs[col],
exprlen );
outstr[exprlen] = (char)0;
printf ( "%s\n", outstr );
}
/.
Write out the data.
./
switch ( xtypes[col] )
{
case SPICE_CHR:
ekgc_c ( col, row, 0, LNSIZE,
cdata, &null, &found );
if ( !null )
{
printf ( "%s\n", cdata );
}
break;
case SPICE_DP:
ekgd_c ( col, row, 0,
&ddata, &null, &found );
if ( !null )
{
printf ( "%f\n", ddata );
}
break;
case SPICE_INT:
ekgi_c ( col, row, 0,
&idata, &null, &found );
if ( !null )
{
printf ( "%d\n", cdata );
}
break;
case SPICE_TIME:
/.
The item is a time value. Convert it
to UTC for output.
./
ekgd_c ( col, row, 0,
&tdata, &null, &found );
if ( !null )
{
et2utc_c ( tdata, "C", 3,
TIMELEN, utc );
printf ( "%s\n", utc );
}
break;
default:
;
}
/.
Handle null values here.
./
if ( null )
{
printf ( "%s\n", "<Null>" );
}
/.
End of data type switch.
./
}
/.
We're done with the column having index col.
./
}
/.
We're done with the row having index row.
./
}
/.
We either processed the query or ekfind_c detected an
error.
./
}
/.
We either parsed the SELECT clause or ekpsel_c detected an
error.
./
}
}
1) Currently, column names are the only supported expressions.
1) Parse failures do not cause this routine to signal errors;
instead, the error and errmsg outputs indicate invalid
QUERIES.
2) Queries cannot be parsed correctly unless at least one EK
is loaded.
None.
N.J. Bachman (JPL)
None.
-CSPICE Version 2.1.0, 02-SEP-1999 (NJB)
Local type logical variable now used for error flag used in
interface of ekpsel_.
-CSPICE Version 2.0.0, 19-JUL-1999 (NJB)
The data types of the tabs and cols arguments were changed
to (void *), and associated string length arguments were added.
This style of interface for string arrays is now standard within
CSPICE.
Some corrections of the header comments were made.
-CSPICE Version 1.0.0, 21-FEB-1999 (NJB)
parse select clause of EK query