Function explain_data_prepare

lib-src/sqlite/shell.c:12956–13034

** If compiled statement pSql appears to be an EXPLAIN statement, allocate ** and populate the ShellState.aiIndent[] array with the number of ** spaces each opcode should be indented before it is output. ** ** The indenting rules are: ** ** * For each "Next", "Prev", "VNext" or "VPrev" instruction, indent ** all opcodes that occur between the p2 jump destination and the opcode ** i

**       and "Goto" by 2 spaces.
*/
static void explain_data_prepare(ShellState *p, sqlite3_stmt *pSql){
  const char *zSql;               /* The text of the SQL statement */
  const char *z;                  /* Used to check if this is an EXPLAIN */
  int *abYield = 0;               /* True if op is an OP_Yield */
  int nAlloc = 0;                 /* Allocated size of p->aiIndent[], abYield */
  int iOp;                        /* Index of operation in p->aiIndent[] */

  const char *azNext[] = { "Next", "Prev", "VPrev", "VNext", "SorterNext", 0 };
  const char *azYield[] = { "Yield", "SeekLT", "SeekGT", "RowSetRead",
                            "Rewind", 0 };
  const char *azGoto[] = { "Goto", 0 };

  /* Try to figure out if this is really an EXPLAIN statement. If this
  ** cannot be verified, return early.  */
  if( sqlite3_column_count(pSql)!=8 ){
    p->cMode = p->mode;
    return;
  }
  zSql = sqlite3_sql(pSql);
  if( zSql==0 ) return;
  for(z=zSql; *z==' ' || *z=='\t' || *z=='\n' || *z=='\f' || *z=='\r'; z++);
  if( sqlite3_strnicmp(z, "explain", 7) ){
    p->cMode = p->mode;
    return;
  }

  for(iOp=0; SQLITE_ROW==sqlite3_step(pSql); iOp++){
    int i;
    int iAddr = sqlite3_column_int(pSql, 0);
    const char *zOp = (const char*)sqlite3_column_text(pSql, 1);

    /* Set p2 to the P2 field of the current opcode. Then, assuming that
    ** p2 is an instruction address, set variable p2op to the index of that
    ** instruction in the aiIndent[] array. p2 and p2op may be different if
    ** the current instruction is part of a sub-program generated by an
    ** SQL trigger or foreign key.  */
    int p2 = sqlite3_column_int(pSql, 3);
    int p2op = (p2 + (iOp-iAddr));

    /* Grow the p->aiIndent array as required */
    if( iOp>=nAlloc ){
      if( iOp==0 ){
        /* Do further verfication that this is explain output.  Abort if
        ** it is not */
        static const char *explainCols[] = {
           "addr", "opcode", "p1", "p2", "p3", "p4", "p5", "comment" };
        int jj;
        for(jj=0; jj<ArraySize(explainCols); jj++){
          if( strcmp(sqlite3_column_name(pSql,jj),explainCols[jj])!=0 ){
            p->cMode = p->mode;
            sqlite3_reset(pSql);
            return;
          }
        }
      }
      nAlloc += 100;
      p->aiIndent = (int*)sqlite3_realloc64(p->aiIndent, nAlloc*sizeof(int));
      if( p->aiIndent==0 ) shell_out_of_memory();