I386LINUX/util/I386LINUX/doc/postgresql/html/catalog-pg-statistic.html

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  43 >PostgreSQL 7.4.1 Documentation</TH
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  67 >Chapter 43. System Catalogs</TD
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  91 CLASS="SECT1"
  92 ><H1
  93 CLASS="SECT1"
  94 ><A
  95 NAME="CATALOG-PG-STATISTIC"
  96 >43.27. <TT
  97 CLASS="STRUCTNAME"
  98 >pg_statistic</TT
  99 ></A
 100 ></H1
 101 ><A
 102 NAME="AEN51272"
 103 ></A
 104 ><P
 105 >   The catalog <TT
 106 CLASS="STRUCTNAME"
 107 >pg_statistic</TT
 108 > stores statistical data about
 109    the contents of the database.  Entries are created by
 110    <TT
 111 CLASS="COMMAND"
 112 >ANALYZE</TT
 113 > and subsequently used by the query planner.
 114    There is one entry for each table column that has been analyzed.
 115    Note that all the statistical data is inherently approximate,
 116    even assuming that it is up-to-date.
 117   </P
 118 ><P
 119 >   Since different kinds of statistics may be appropriate for different
 120    kinds of data, <TT
 121 CLASS="STRUCTNAME"
 122 >pg_statistic</TT
 123 > is designed not
 124    to assume very much about what sort of statistics it stores.  Only
 125    extremely general statistics (such as nullness) are given dedicated
 126    columns in <TT
 127 CLASS="STRUCTNAME"
 128 >pg_statistic</TT
 129 >.  Everything else
 130    is stored in <SPAN
 131 CLASS="QUOTE"
 132 >"slots"</SPAN
 133 >, which are groups of associated columns whose
 134    content is identified by a code number in one of the slot's columns.
 135    For more information see
 136    <TT
 137 CLASS="FILENAME"
 138 >src/include/catalog/pg_statistic.h</TT
 139 >.
 140   </P
 141 ><P
 142 >   <TT
 143 CLASS="STRUCTNAME"
 144 >pg_statistic</TT
 145 > should not be readable by the
 146    public, since even statistical information about a table's contents
 147    may be considered sensitive.  (Example: minimum and maximum values
 148    of a salary column might be quite interesting.)
 149    <A
 150 HREF="view-pg-stats.html"
 151 ><TT
 152 CLASS="STRUCTNAME"
 153 >pg_stats</TT
 154 ></A
 155 >
 156    is a publicly readable view on
 157    <TT
 158 CLASS="STRUCTNAME"
 159 >pg_statistic</TT
 160 > that only exposes information
 161    about those tables that are readable by the current user.
 162   </P
 163 ><DIV
 164 CLASS="TABLE"
 165 ><A
 166 NAME="AEN51287"
 167 ></A
 168 ><P
 169 ><B
 170 >Table 43-27. <TT
 171 CLASS="STRUCTNAME"
 172 >pg_statistic</TT
 173 > Columns</B
 174 ></P
 175 ><TABLE
 176 BORDER="1"
 177 CLASS="CALSTABLE"
 178 ><COL><COL><COL><COL><THEAD
 179 ><TR
 180 ><TH
 181 >Name</TH
 182 ><TH
 183 >Type</TH
 184 ><TH
 185 >References</TH
 186 ><TH
 187 >Description</TH
 188 ></TR
 189 ></THEAD
 190 ><TBODY
 191 ><TR
 192 ><TD
 193 ><TT
 194 CLASS="STRUCTFIELD"
 195 >starelid</TT
 196 ></TD
 197 ><TD
 198 ><TT
 199 CLASS="TYPE"
 200 >oid</TT
 201 ></TD
 202 ><TD
 203 ><TT
 204 CLASS="LITERAL"
 205 ><A
 206 HREF="catalog-pg-class.html"
 207 ><TT
 208 CLASS="STRUCTNAME"
 209 >pg_class</TT
 210 ></A
 211 >.oid</TT
 212 ></TD
 213 ><TD
 214 >The table that the described column belongs to</TD
 215 ></TR
 216 ><TR
 217 ><TD
 218 ><TT
 219 CLASS="STRUCTFIELD"
 220 >staattnum</TT
 221 ></TD
 222 ><TD
 223 ><TT
 224 CLASS="TYPE"
 225 >int2</TT
 226 ></TD
 227 ><TD
 228 ><TT
 229 CLASS="LITERAL"
 230 ><A
 231 HREF="catalog-pg-attribute.html"
 232 ><TT
 233 CLASS="STRUCTNAME"
 234 >pg_attribute</TT
 235 ></A
 236 >.attnum</TT
 237 ></TD
 238 ><TD
 239 >The number of the described column</TD
 240 ></TR
 241 ><TR
 242 ><TD
 243 ><TT
 244 CLASS="STRUCTFIELD"
 245 >stanullfrac</TT
 246 ></TD
 247 ><TD
 248 ><TT
 249 CLASS="TYPE"
 250 >float4</TT
 251 ></TD
 252 ><TD
 253 >&nbsp;</TD
 254 ><TD
 255 >The fraction of the column's entries that are null</TD
 256 ></TR
 257 ><TR
 258 ><TD
 259 ><TT
 260 CLASS="STRUCTFIELD"
 261 >stawidth</TT
 262 ></TD
 263 ><TD
 264 ><TT
 265 CLASS="TYPE"
 266 >int4</TT
 267 ></TD
 268 ><TD
 269 >&nbsp;</TD
 270 ><TD
 271 >The average stored width, in bytes, of nonnull entries</TD
 272 ></TR
 273 ><TR
 274 ><TD
 275 ><TT
 276 CLASS="STRUCTFIELD"
 277 >stadistinct</TT
 278 ></TD
 279 ><TD
 280 ><TT
 281 CLASS="TYPE"
 282 >float4</TT
 283 ></TD
 284 ><TD
 285 >&nbsp;</TD
 286 ><TD
 287 >The number of distinct nonnull data values in the column.
 288       A value greater than zero is the actual number of distinct values.
 289       A value less than zero is the negative of a fraction of the number
 290       of rows in the table (for example, a column in which values appear about
 291       twice on the average could be represented by <TT
 292 CLASS="STRUCTFIELD"
 293 >stadistinct</TT
 294 > = -0.5).
 295       A zero value means the number of distinct values is unknown.
 296       </TD
 297 ></TR
 298 ><TR
 299 ><TD
 300 ><TT
 301 CLASS="STRUCTFIELD"
 302 >stakind<VAR
 303 CLASS="REPLACEABLE"
 304 >N</VAR
 305 ></TT
 306 ></TD
 307 ><TD
 308 ><TT
 309 CLASS="TYPE"
 310 >int2</TT
 311 ></TD
 312 ><TD
 313 >&nbsp;</TD
 314 ><TD
 315 >       A code number indicating the kind of statistics stored in the
 316        <VAR
 317 CLASS="REPLACEABLE"
 318 >N</VAR
 319 >th <SPAN
 320 CLASS="QUOTE"
 321 >"slot"</SPAN
 322 > of the
 323        <TT
 324 CLASS="STRUCTNAME"
 325 >pg_statistic</TT
 326 > row.
 327       </TD
 328 ></TR
 329 ><TR
 330 ><TD
 331 ><TT
 332 CLASS="STRUCTFIELD"
 333 >staop<VAR
 334 CLASS="REPLACEABLE"
 335 >N</VAR
 336 ></TT
 337 ></TD
 338 ><TD
 339 ><TT
 340 CLASS="TYPE"
 341 >oid</TT
 342 ></TD
 343 ><TD
 344 ><TT
 345 CLASS="LITERAL"
 346 ><A
 347 HREF="catalog-pg-operator.html"
 348 ><TT
 349 CLASS="STRUCTNAME"
 350 >pg_operator</TT
 351 ></A
 352 >.oid</TT
 353 ></TD
 354 ><TD
 355 >       An operator used to derive the statistics stored in the
 356        <VAR
 357 CLASS="REPLACEABLE"
 358 >N</VAR
 359 >th <SPAN
 360 CLASS="QUOTE"
 361 >"slot"</SPAN
 362 >.  For example, a
 363        histogram slot would show the <TT
 364 CLASS="LITERAL"
 365 >&lt;</TT
 366 > operator
 367        that defines the sort order of the data.
 368       </TD
 369 ></TR
 370 ><TR
 371 ><TD
 372 ><TT
 373 CLASS="STRUCTFIELD"
 374 >stanumbers<VAR
 375 CLASS="REPLACEABLE"
 376 >N</VAR
 377 ></TT
 378 ></TD
 379 ><TD
 380 ><TT
 381 CLASS="TYPE"
 382 >float4[]</TT
 383 ></TD
 384 ><TD
 385 >&nbsp;</TD
 386 ><TD
 387 >       Numerical statistics of the appropriate kind for the
 388        <VAR
 389 CLASS="REPLACEABLE"
 390 >N</VAR
 391 >th <SPAN
 392 CLASS="QUOTE"
 393 >"slot"</SPAN
 394 >, or null if the slot
 395        kind does not involve numerical values.
 396       </TD
 397 ></TR
 398 ><TR
 399 ><TD
 400 ><TT
 401 CLASS="STRUCTFIELD"
 402 >stavalues<VAR
 403 CLASS="REPLACEABLE"
 404 >N</VAR
 405 ></TT
 406 ></TD
 407 ><TD
 408 ><TT
 409 CLASS="TYPE"
 410 >anyarray</TT
 411 ></TD
 412 ><TD
 413 >&nbsp;</TD
 414 ><TD
 415 >       Column data values of the appropriate kind for the
 416        <VAR
 417 CLASS="REPLACEABLE"
 418 >N</VAR
 419 >th <SPAN
 420 CLASS="QUOTE"
 421 >"slot"</SPAN
 422 >, or null if the slot
 423        kind does not store any data values.  Each array's element
 424        values are actually of the specific column's data type, so there
 425        is no way to define these columns' type more specifically than
 426        <TT
 427 CLASS="TYPE"
 428 >anyarray</TT
 429 >.
 430       </TD
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