It’s usually when folks build up SQL statements.
When you add and value = "Toyota"
you don’t have to worry about whether there is a condition before or just WHERE. The optimiser should ignore it
No magic, just practical
Example Code:
commandText = "select * from car_table where 1=1";
if (modelYear <> 0) commandText += " and year="+modelYear
if (manufacturer <> "") commandText += " and value="+QuotedStr(manufacturer)
if (color <> "") commandText += " and color="+QuotedStr(color)
if (california) commandText += " and hasCatalytic=1"
Otherwise you would have to have a complicated set of logic:
commandText = "select * from car_table"
whereClause = "";
if (modelYear <> 0)
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "year="+modelYear;
}
if (manufacturer <> "")
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "value="+QuotedStr(manufacturer)
}
if (color <> "")
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "color="+QuotedStr(color)
}
if (california)
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "hasCatalytic=1"
}
if (whereClause <> "")
commandText = commandText + "WHERE "+whereClause;